NSW lifesavers embedded with the NSW SES assist with a flood rescue in Penrith. Picture / NSW SES

The East Coast Low which has caused all the weather drama in New South Wales is finally moving away, taking much of the rain with it.

But in exceedingly unwelcome news, forecasters have said another low is brewing and that could bring yet more heavy rain on the weekend to exactly the same areas that are already flooded.

A month's worth of rain could drench NSW in the coming week. But that's actually less than what fell over the last few days, showing just want a mammoth rain event Sydney and the surrounding areas have been through.

The current system may be moving away but it's leaving a trail of destruction in its wake and further flooding fears.

There are around 70 evacuation orders in place for about 40 suburbs in and near Sydney and nine evacuation centres have been set up for the at least 30,000 people who cannot remain in their homes. Meanwhile, scores of roads and railway lines have been flooded.

The State Emergency Service (SES) has received more than 1500 requests for help and performed nearly 120 rescues. The Australian Defence Force has made available 100 troops to help in rescue efforts and provided two helicopters to help in the search for stranded people.

One person died when their kayak overturned in the Parramatta River while a pregnant women was among those rescued.

Talking to Channel 9's Today programme on Monday, Weatherzone meteorologist Ben Domensino said Sydney was getting the equivalent rainfall of all the water in Sydney Harbour each day during the current weather event.

"It is hard to fathom that we are seeing a rain event of this magnitude hitting this part of Australia once again.

"We have had several of them already this year but this one, in particular, has been exceptional heavy for areas near and south of Sydney."

Holsworthy Barracks, in Sydney's south, recorded 128mm of rain from 9am Monday, bringing its three-day total to 466mm. Lucas Heights, in the Sutherland Shire, is now sitting at more than half a metre of rain in 72 hours.

"Before this rain arrived, we had catchments that were still fairly wet and close to capacity. So it hasn't taken a lot of rain for the rivers to respond and go back into a major flood," said Sky News Weather senior meteorologist Tom Saunders.

Showers will remain for Sydney over the coming days, but the totals will be far lower compared to the weekend. The city could see 15-20mm on Tuesday, less than 5mm on Wednesday and up to 15mm on Thursday.

With the system moving north, it's these areas that could see heavier falls. Newcastle, for instance, could record 35-50mm on Tuesday before rainfall levels weaken. Although there will be showers all week. Port Macquarie could see up to 25mm on Tuesday and then 25-45mm on Wednesday.

But weather trouble is brewing once again.

"It looks like we'll get another couple of Tasman low-pressure systems forming up through the weekend," said Saunders.

"One could form closer to the coast and perhaps even bring a burst of heavy rain again, most likely for the southern and central NSW coast."

But Saunders cautioned that the potential lows were still a long way off and their energy and location could change and so the forecast could change.

The current Bureau of Meteorology outlook suggest showers on Saturday increasing for Sunday.

More than 30,000 people have been told to evacuate their homes as Sydney's flood emergency continues.

Emergency Management Minister Murray Watt declared a state of natural disaster for 23 NSW local government areas about 11pm overnight - meaning impacted residents may be eligible for payments.

"We have seen some of these impacted communities being hit by floods for a third and fourth time in 18 months, which is extremely distressing to the residents of these communities," Senator Watt said.

The Hawkesbury suburbs of Richmond, Windsor, Sackville and Wisemans Ferry have been impacted hardest and will likely see extensive flooding in the coming 24 hours.

Late on Monday night, parts of Chipping Norton and Lower Portland were ordered to leave their homes by 11.45pm and 2am respectively.

Rapid river level rises were detected upstream of Liverpool, prompting the Bureau of Meteorology to issue a flood warning for Liverpool and Milperra.

The NSW SES immediately ordered residents in low-lying parts of Woronora and Bonnet Bay to evacuate.

Those in the following parts of Woronora are being ordered to evacuate as soon as they can are Harrison Ave, McKinley Ave, Washington Drive, Wilson Place.

Those in the following parts of Bonnet Bay are being ordered to evacuate by 8pm: Johnson Close, Arthur Place and properties on Lower Washington Drive backing on to Johnson Close.

The Bureau says major flooding is possible at Liverpool and Milperra on Monday evening.

People living near Warwick Farm Racecourse, as well as parts of Chipping Norton, Georges Hall, Moorebank and Lansvale were all told to leave by 9pm.

All those living on Governor Macquarie Drive between Barry Rd and Newbridge Rd, bordering west of Riverside Rd in Chipping Norton, were told to leave by 11.45pm.

The same message was sent to people living on Governor Macquarie Drive bounded by Georges River on the west and north and by Ernest St on the east including South Park and Chipping Norton Public School.

Some people on West Portland Rd in Lower Portland were also told to evacuate.

Earlier on Monday, evacuation orders were issued for parts of Cattai, Sackville North, Londonderry and Richards.

NSW SES updated their flood evacuation notice to include Wisemans Ferry at 4pm on Monday afternoon.

Authorities have pleaded with residents to cancel holidays and avoid floodwaters, as parts of NSW and the Illawarra continue to be inundated with rescue requests.

In a press conference on Monday morning, NSW Premier Dominic Perrottet said that a massive 71 evacuation orders and 64 evacuation warnings were in place, with 83 flood rescues and 1593 requests for assistance lodged since 9pm Sunday.

While flood waters have peaked, or are close to peaking in Menangle, and North Richmond, the situation is expected to worsen for the Windsor and the Lower Portland areas. Major flooding has been predicted to hit on Monday afternoon, before it moves downstream to Sackville and Wisemans Ferry.

Perrottet also issued a stern warning for affected residents to abide by instructions and in particular, to strictly avoid driving into flood waters.

"If there is an evacuation warning in place, please get ready to evacuate. If there is an evacuation order in place, please leave immediately," he said.

"These instructions, warnings, orders, they are not in place for the sake of it."

Despite three days of devastating rain, Minister for Emergency Services and Resilience and Minister for Flood Recovery Steph Cook warned the state was "not quite out of the woods yet".

She said a Commonwealth announcement for wider recovery measures would be announced on Tuesday. However, the process would be kickstarted where it was possible to do so.

The Australian Defence Force has received requests for additional support under the Commonwealth disaster recovery plan.

"We have SES communities at the Georges River area, looking at the impact of this latest flooding on people's homes, their businesses and the local infrastructure, working closely with councils, of course, to make sure that is all captured," said Cook.

"That will form the basis of our discussions with the Federal Government in relation to rolling up support for communities as we look to get people back on their feet."

Speaking on ABC's News Breakfast, the Federal emergency management minister Murray Watt said he believed the state government would declare a state of disaster. This would allow the NSW government greater powers in administering directives to help affected areas.

"At this stage, the advice is this particular disaster, while severe, does not reach the level of the threshold required to invoke a national emergency declaration," he said.

"Having said that, it is likely the NSW government will declare this flood as a disaster from a NSW perspective."

Heavy military vehicles and personnel were rolled out onto Sydney streets on Monday to assist with damaging flooding.

Over 100 Australian Defence Force (ADF) personnel have been tasked with assisting evacuations and conducting welfare door knocks.

Two ADF helicopters were also deployed for the purpose of night searches as water levels continued to threaten communities.

Prime Minister Anthony Albanese urged those affected to stay safe after returning from war-torn Ukraine on Monday afternoon (AEST).

Albanese visited Ukraine over the weekend where he met President Volodymyr Zelensky.

The Prime Minister confirmed he had been briefed on the situation by Perrottet and Emergency Management Minister Murray Watt.

"Have crossed into Poland from Ukraine and left radio silence," Albanese tweeted.

"It's a constantly changing situation. Check @NSWSES and @BOM_NSW for the latest advice and stay safe."

A family of five were plucked from danger on Monday evening after their car was nearly submerged in floodwaters.

A pregnant mum was among those saved by specialist Fire and Rescue NSW officers at the corner of The River Rd and Prince St in Revesby Heights just before 5.30pm.

The crew guided one woman from a car to safety and then discovered the family in another vehicle, stranded in the middle of the road.

A father, his pregnant wife, and three children, all believed aged under six, were unable to escape the vehicle, due to floodwaters lapping at the doors.

The fire crew, trained in swift-water rescues, waded out to the vehicle and fitted life jackets to the family.

The firefighters safely carried the children in their arms as they guided the parents through the floodwaters to waiting relatives nearby.

No one was hurt in the incident.

Concerns have also been made for a bulk carrier vessel in Portland Bay which departed Wollongong on Monday morning.

Carrying 21 crew members, the ship had lost power near the Royal National Park, with fears it risked crashing into a cliff face a mere 1km away.

#WATCH // @Lifesaverhelo is responding to a stranded container ship off the Royal National Park. Conditions are currently too rough to attempt to winch the crew from the ship. The ship has no power and is currently 1nm offshore. IRBS from #thirroulslsc and a jetski are on standby pic.twitter.com/O5s5TViek5

Bulk carrier Portland Bay looks out of control very close to running aground near Sydney’s Royal National Park. pic.twitter.com/LKB9Zaho78

Perrottet said the vessel was in a "very precarious position". However, the ship was currently double anchored, with a rescue plan in place. Two tug boats have been sent to direct the ship away from the cliff face.

In an update from Surf Life Saving NSW, it said the conditions were too rough for Westpac Rescue Helicopters, who were unable to winch the crew from the stranded ship.

The Bureau of Meteorology has issued a number of severe weather warnings in the wake of the East Coast Low.

The weather system touched land late on Sunday and is forecast to linger for another day, before steadily moving north.

The low has weakened, but the trough is still directing humid air onshore, causing moderate to at times heavy rainfall. Drier air will push gradually northwards up the NSW coast through the afternoon, clearing most of the rain out of the Illawarra, Blue Mountains and Sydney regions by late this evening.

The BOM said although rain rates have generally eased, heavy falls are still possible today in the Illawarra region, the Blue Mountains, Sydney, central coast and parts of the Hunter. Six-hourly rainfall totals between 60 to 100mm are possible and that could lead to flooding.

The low is causing very heavy surf which may lead to localised damage and coastal erosion.

Significant wave heights of over five meters are likely, with peak periods around 11 seconds.

A fierce East Coast Low weather system is battering a huge stretch of the New South Wales coast.

But it's saved the majority of its weather wrath for Sydney and the Illawarra.

Forecasters have said the horrendous conditions will continue on Monday, with up to 100mm of rain due to fall in Sydney, 150mm possible in Wollongong and up to 200mm in isolated pockets elsewhere.

Those totals can be added to the huge amount of rain that's fallen over the last few days.

One man has died and flash and riverine flooding has occurred in and beyond Sydney.

"The next 24 hours will decide how high the floods peak along the Hawkesbury River such as around Richmond, where the water levels have already risen substantially," said Sky News Weather meteorologist Rob Sharp.

"And they could go a lot further than that, depending on how much falls with this system."