Towns urged to evacuate as severe weather threatens 800km of NSW coastline

More NSW communities are preparing to evacuate as heavy rainfall continues to threaten areas already battling rising floodwaters.

The NSW State Emergency Service (SES) has ordered parts of Camden, on the southwest outskirts of Sydney, to evacuate by 9pm on Monday.

Picton, southwest of Sydney, was issued with an evacuation flood warning early on Monday afternoon. This was followed by later evacuation warnings for Emu Plains and Mulgoa.

Numerous flood warnings are in place across NSW as heavy rainfall continues to plague saturated communities across the state. The Hawkesbury and Nepean regions are in danger of more moderate to major flooding.

The Bureau of Meteorology (BoM) has updated a severe weather warning for the coast stretching about 800km, from north of Taree to Bega.

There's a risk of thunderstorms, large and powerful surf and flooding at levels similar to those seen last week.

Six-hourly rainfall totals between 70mm to 120mm are possible, which could lead to flash flooding in Greater Sydney, Mid-North Coast, Hunter, Illawarra, South Coast, and parts of the Tablelands.

Thunderstorms could also bring intense rain to the Northern Rivers, and damaging winds and large hail could hit Lismore and nearby towns trying to clean up.

Nepean and Hawkesbury flood warnings

The Nepean River at Menangle Bridge may rise as high as 12.2 metres on Monday, the bureau has warned.

The Hawkesbury River at North Richmond is experiencing major flooding and could reach 13 metres, with further rises possible.

The Hawkesbury River at Windsor, where moderate flooding is already occurring, may rise to 12.2 metres on Monday night and into Tuesday, BoM said.

There is a major flood warning for the Weir River and minor to moderate flood warnings in place for the following: Lower Macintyre River, Snowy River, Macquarie River to Bathurst, Richmond River, Barwon River,m Paroo River, Lachlan River, Orara River, Tuggerah Lake, Shoalhaven River, Georges River, Hunter River, Woolombi Brook, Macleay River, Bellinger River and Clarence River.

The State Emergency Service had another 550 calls for help overnight and performed nine flood rescues.

SES Deputy Commissioner Daniel Austin said they are expecting to see “widespread, major flooding” on Monday and urged people to heed advice and warnings.

"We're certainly on high alert from the Mid North Coast down into the Shoalhaven," he told the Nine Network.

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"We are watching exceptionally closely a number of catchments ... around the Hawkesbury and Central Coast and places.

"The water hasn't retreated yet. We're now going to see more flooding on top of what we've already seen."

Rain is causing significant travel delays with cancellations expected on most Sydney Trains, NSW TrainLink Intercity and Regional trains services.

NSW Premier apologises to flood victims

Premier Dominic Perrottet has apologised to thousands of people in the Northern Rivers district, whose homes and businesses were destroyed when towns like Lismore and Ballina were inundated by floodwaters last week.

Many have since struggled to access basics such as food, water, power, fuel, phones, ATMs, the internet and medical supplies.

"I'm very sorry ... but we're doing everything that we can," Mr Perrottet told the Nine Network from Lismore.

"Some of those areas will look back at this and say it could have been done better but ... we're doing absolutely everything we can to provide care and support for those who need it to get those essential supplies in," he said.

The emergency response would be reviewed, he added.

Floods have claimed six lives in NSW, including four in Lismore.

The Australia Defence Force is helping with a "mammoth" clean-up with 2000 personnel on the ground across the Northern Rivers.

"We're getting supplies in. We're getting food in," Mr Perrottet said.

Around 2000 of the 3500 homes assessed so far in the Northern Rivers are no longer habitable, increasing the need for short-term and medium-to-long-term accommodation.

Telstra on Monday said it had restored about 80 per cent of mobile coverage for communities in northern NSW and 75 per cent of landline connections.

But some areas remained inaccessible due to continued flooding, road damage or a lack of electricity that is hampering the work of around 1000 technicians.

The northern NSW communities of Kingscliff, Main Arm, Mullumbimby, Ocean Shores, Tucabia, Uki and Wooli are among those still having issues with communications.

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