Severe thunderstorms, damaging winds and heavy rainfall have smashed large parts of NSW including the Illawarra and towards the Victorian border since Tuesday.

Huge amounts of rain has fallen in the past few days, with almost 300 millimetres recorded at Point Perpendicular (290.8mm) and 249mm at Jervis Bay.

SES volunteers conducted 13 flood rescues, including in Dunmore, Nowra, Lake Conjola. Some rescues occurred after people drove into floodwaters. Nobody was injured.

At least 40 homes - in Lake Conjola and Wrights Beach at St Georges Basin - on the South Coast have been inundated by floodwaters. There are no reports of homes being inundated in the Illawarra.

Bega River peaked at 6.35 metres at 8.30pm on Wednesday and SES volunteers doorknocked to inform residents.

Watch and act alerts remain in place for areas around Lake Conjola and Bega.

"There's another low sitting off the far South Coast which is expected to impact the Bega, Moruya areas again in the next couple of hours," an SES spokeswoman said at 7am on Thursday.

Many weather warnings are in place, including:

SES crews have received 1056 emergency calls for help during the past 24 hours, with 505 of those in the 'south eastern zone' which covers the Illawarra, Southern Highlands and South Coast to the border.

Rainfall readings so far this week to 7am on Thursday:

"The low sitting off the far South Coast is expected to hit land mid-morning, bringing with it a renewed risk of moderate flooding in the Bega region," a SES spokeswoman said.

"The NSW SES is urging people to assess conditions before traveling on the roads, not to walk, ride or drive through flood waters and to heed any warnings."