Schools have closed, roads are flooded and SES volunteers have been door-knocking across southern Sydney, as rain continues to fall and thousands are ordered to evacuate.

Chipping Norton and Camden residents were the latest warned to leave on Thursday.

The SES said all people must be out of Chipping Norton by 3pm as the areas would be isolated once floodwaters reached 2.4 metres at Milperra.

The order applies to properties in Newbridge Road between Riverside Road and east to Georges River, Davy Robinson Drive, Rickard Road and Arthur Street.

In Camden, residents in Exeter Street west of John Street, Milford Road (Camden West) and Peter Avenue between Onslow Avenue and Belgenny Avenue had until 6pm to leave.

• See all of the NSW SES’s evacuation orders and warnings here

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The alerts came after people in parts of Woronora and Bonnet Bay in the city’s south were told to evacuate in the morning.

Warnings for possible evacuations were also in place for Stuarts Point on the mid-north coast, and Stonequarry Creek, Picton and Camden in southwestern Sydney.

“We ask the community to continue to be vigilant. This is a highly dynamic situation,” NSW SES Acting Commissioner Daniel Austin said on Thursday afternoon.

“These events are moving exceptionally quickly, as was witnessed in the Illawarra this morning where we saw in the space of about three-quarters-of-an-hour significant downpours, significant flash flooding, and a number of properties impacted by those flash events.”

The SES has responded to almost 700 requests for assistance and conducted 25 rescues, the majority for people caught out by flash flooding. That included six at Illawarra after “exceptionally sharp, short bursts of rain” on Thursday morning.

Elsewhere, a helicopter winched a man to safety after his vehicle became trapped in floodwaters at Kangaroo Valley, on the south coast.

Heavy rain fell across much of NSW throughout Thursday.

Sydney has already topped its average annual rainfall, despite it being only April. More than 114 millimetres fell the Bureau of Meteorology’s Observatory Hill site in The Rocks in the 24 hours to 9am Wednesday, taking its total for the year to 1226.8 millimetres, above the annual average of 1213.4 millimetres.

NSW has been hit by repeat floods in recent months, with the northern rivers area devastated by two deluges within weeks while Sydney endures an almost constant drenching.

Authorities issued a severe weather warning on Thursday for southern and central NSW, metropolitan Sydney, the Illawarra, the south coast, the central and southern tablelands, and parts of the Hunter.

There was major flooding at Menangle and the Upper Nepean by Thursday afternoon. Flood levels at Menangle could surpass the record set in April 1988, Bureau of Meteorology senior hydrologist Ailsa Schofield said.

“There is also the significant risk of continued flash flooding in the greater Sydney, Upper Hunter, Illawarra and south coast areas from today and into the weekend,” Ms Scofield said.

“I’m really urging residents to stay up to date with the local weather and warning information and stay safe.”

Major flooding – higher than seen in March – is expected late on Thursday into Friday at Wallacia. Major flooding at Camden is also expected to be higher than it was last month.

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The weather bureau warned of the potential for major flooding along the Georges River at Liverpool and Milperra on Thursday afternoon, while there are also warnings for the Hawkesbury, Colo and Cooks rivers.

Heavy rain also fell on the south coast and southern tablelands overnight, while the wet weather was extending across Sydney, the central tablelands and Hunter region on Thursday.

Six-hourly rainfall totals up to 180 millimetres were likely in some coastal areas, the BOM warned.

Numerous areas around Sydney and the Illawarra had more than 100 millimetres in the 24 hours from 9am on Wednesday.

There were significant falls in the metropolitan area at Rose Bay (140 millimetres), Little Bay (140 millimetres), Belrose (117 millimetres) and Marrickville (110 millimetres), while further south in the Illawarra and south coast there were downpours at Darkes Forest (193 millimetres), Macquarie Pass (184 millimetres), Bodalla (127 millimetres) and Nowra (125 millimetres).

There is an increased risk of landslides, according to the BOM.

Several schools were closed in Sydney’s south, the Illawarra and the south coast on Thursday, including Dapto High School, Kanahooka High School, Kurnell Public School, Terara Public School, and Woronora River Public School.

Mr Austin also urged people to limit all non-essential travel and re-think movements over the school holidays.

Liverpool Mayor Ned Mannoun told Sydney radio 2GB on Thursday there was a sense of deja vu in the area following flooding last month.

Residents are invited to pick up sandbags.

“We know what’s going to happen, we just hope it won’t get worse than last time,” Mr Mannoun said.

Moderate flooding could occur on the Colo River at Putty Road.

The rain is expected to ease on Friday but the flood risk will remain throughout the week.

-with AAP