The state has been hit by repeat floods in recent months, with the Northern Rivers area devastated by two deluges within weeks and Sydney enduring an almost constant drenching.

An evacuation order has been issued for residents in low-lying areas of Woronora and Bonnet Bay in Sydney’s south, and residents in parts of the southwest have been told to prepare to evacuate.

Flood watches have been issued around NSW with minor to major flooding forecast in several catchments.

Water is spilling at Warragamba Dam, which was already at capacity before the rain began.

Major flooding is expected on the Nepean River with Menangle, Wallacia, and possibly Camden expected to be impacted over the coming days.

“We have forecast for a major flood peak to occur later this evening (at Menangle), and that will be near the April 1988 flood level … higher than the March (2021 and 2022) flood levels,” Bureau of Meteorology senior hydrologist Ailsa Schofield said on Thursday.

The SES has responded to almost 700 requests for assistance and conducted 25 rescues, the majority for people caught out by flash flooding.

“We have seen exceptionally sharp, short bursts of rain that have created significant flash flooding,” acting commissioner Daniel Austin said.

The Hawkesbury, Nepean, Georges and Woronora Rivers are at risk of major flooding.

In Liverpool and Milperra in Sydney’s west, the Georges River is expected to rise above four metres in the late afternoon high tide.

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.

Minor flooding is forecast in several catchments around NSW, including along the Upper Coxs, Macdonald, Parramatta, Shoalhaven, Clyde, Moruya and Deua Rivers as well as St Georges Basin.

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.

Six-hourly rainfall totals up to 180mm are likely in some coast areas, the BOM warned.

Cronulla, south of Sydney’s centre, recorded 107mm in three hours overnight.

In the Illawarra, Mount Pleasant received 112mm and Rixons Pass 79mm in less than four hours on Thursday.

Sydney has received more than its average annual rainfall at the Bureau of Meteorology’s Observatory Hill site in The Rocks despite it only being early April.

More than 114mm fell there in the 24 hours up to 9am on Thursday, and a further 18.4mm in the four hours that followed, taking its total for the year to 1245.2mm, above the annual average of 1213.4mm.

Several schools have closed in Sydney’s south, the Illawarra and the South Coast, including Dapto High School, Kanahooka High School, Kurnell Public School, Terara Public School, and Woronora River Public School.

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