At least 40 homes in Lake Conjola have been inundated by floodwaters, and one or two in Wrights Beach at St Georges Basin.

There are no reports of homes being inundated in the Illawarra.

More heavy rain is predicted to impact Illawarra and the South Coast on Wednesday afternoon and evening, with up to 300 millimetres possible.

The SES warns, this will result in further flash flooding.

Flood rescues have been undertaken in Nowra after cars drove into floodwaters. Other people were rescued from a home at Wrights Beach and a couple and their dog were rescued from a caravan at Lake Conjola.

Nobody was injured during the rescues.

Significant rainfalls were recorded during a 24 hour period overnight on Tuesday, including 226.8mmin Point Perpendicular, 225mm in Jervis Bay and 196.4mm in Ulladulla

"This led to localised flash flooding in a number of areas, particularly St Georges Basin, Wrights Beach and Lake Conjola," SES Chief Superintendent Dallas Burnes said.

"The South Coast is getting smashed," a SES spokeswoman said.

Rainfalls were far less in the Illawarra with Kiama the wettest location with 95.4mm, followed by Albion Park (65.4mm) and Bellambi at 38.2mm

A watch and act alert was issued just after 7am on Wednesday for Lake Conjola and it remained in place at 4pm following very heavy rainfall overnight.

Holiday Haven Lake Conjola manager Brad MacDougall said the rain hasn't stopped since Tuesday night.

"The Lake got up at about 2am over the banks and we were able to get everyone out," he said.

"Most of the holiday vans north of the main road will probably be affected, there's still a lot of water there and it's still going up."

Mr MacDougall urged holidaymakers not to visit the park due to floodwater inundation.

"Hold off on coming down. Don't return to the park until we give you the go ahead," he said.

Lake Conjola resident Anette Gradinger-Walton has been through similar experiences before.

"There is still a lot of water around. My husband just went to the entrance [the Lake's] and the water is obvious raging out but we just just have to ride out the high tide. Hopefully, the water is going to go down," she said on Wednesday morning.

By mid afternoon on Wednesday 15 weather warnings were current for NSW.

Mr Burnes said while significant rainfall is expected in the Moruya and Bega catchments, the greatest concern to authorities is flash flooding along the South Coast.

'Major flood level' river rises are possible for the Bega River, with a watch and act alert expected to be issued for Bega River later on Wednesday. If this occurs SES crews will door know homes in the area.

Homes will only be evacuated in Bega if homes are expected to be inundated.

Emergency crews remain on standby as the weather hits, including Fire and Rescue NSW firefighters from Wollongong, Bulli and Albion Park.

"If you can avoid travel at all in this heavy, storm ridden weather system that would be the best outcome," Mr Burnes said.