Much of coastal Victoria has been battered with an intense downpour of rain that could lead to flash flooding.

Meanwhile, the risk of flooding in NSW remains high despite the rain clearing.

Southern Queensland is also facing its own flood challenges after an earlier deluge resulted in roads being cut off and schools closed.

But it is unlikely to wreak as much havoc there as it did in NSW where almost 7000 people have woken up without electricity on Wednesday morning.

Evacuation orders have affected more than 40,000 people as NSW is hit by once-in-a-generation flooding.

In the past 24 hours alone, the NSW State Emergency Service has been called to more than 1500 jobs.

More than 80 of those were flood rescues.

The SES ordered about 500 people in 200 homes to get out on Tuesday, with boats and helicopters deployed to help them leave.

A family fleeing flooding on the river needed to be rescued twice after the boat evacuating them capsized on Tuesday afternoon.

A mother comforts her children after a family of four, including two young children, whose rescue boat capsized. Photo: AAP

Three SES crews were also on board when the boat overturned as it approached the Sackville Ferry Wharf.

Rivers will rise

Residents have been warned there is no reprieve in sight, at least for the next several days.

Major flooding was occurring early on Wednesday morning northwest of Sydney along the Hawkesbury River at North Richmond, Windsor and on the Colo River.

Tweet from @NSWSES

There was also major flooding on the Nepean River which peaked at 12.85 metres at Menangle, southwest of Sydney, about 10pm on Tuesday.

“This is a weather incident beyond anything we could have comprehended,” Premier Gladys Berejiklian said.

Sunnier skies in coastal NSW will not end flood risks, with rain catchments continuing to flow into bursting rivers.

It will also likely continue to rain on the state’s south coast.

“It is very important to remember that even though we’ll have blue sky and sunshine returning, flooding will continue and the flood risk will continue,” bureau meteorologist Agata Imielska told reporters on Tuesday.

About 280 NSW schools were closed on Tuesday due to the rainfall, with a similar number expected to be shut on Wednesday.

A State Emergency Service rescue crew evacuates a person by boat after rising floodwaters trapped residents, in western Sydney. Photo: AAP

Possible flash flooding in Victoria

Across the border in Victoria, there are serious concerns communities from Mallacoota in Gippsland to Sorrento on the Mornington Peninsula could experience flash flooding.

The whole coastline has been warned to expect heavy rainfall.

So much so that by Wednesday night the Bureau of Meteorology expects between 150 and 200 millimetres of rain to be dumped around the Strzelecki Ranges and Wilsons Promontory.

It’s feared that could lead to flash flooding and damaging winds similar to the NSW South Coast.

A moderate flood warning is in place for the Snowy River, while flood watches remain for parts of Gippsland and the Otway Coast

And an initial moderate flood warning continues for the Genoa River.

Queenslanders urged to ‘be really vigilant’

In Queensland, a major flood warning is active for the Logan River, inland from the Gold Coast, and a moderate flood warning has been issued for the Albert River, both south of Brisbane.

“While rainfall is easing, flood warnings remain in place for the Logan and Albert Rivers,” Logan city authorities said on Tuesday night.

A Swift Water Rescue team from the Queensland Fire and Emergency Services are seen rescuing two men from their car in floodwaters. Photo: AAP

The rain was expected to clear on Wednesday with more settled conditions likely across southern Queensland.

Four homes on the Gold Coast have been evacuated due to landslide risk while more than 100 properties are being inspected for damage in the southeast, Premier Annastacia Palaszczuk told parliament on Tuesday.

More than 20 schools were closed in the region, mainly because of cut roads.

East of Brisbane, Lake Manchester Dam is spilling water and Seqwater has warned those downstream to avoid fast-flowing waterways and flood plains.

The Nerang and Coomera rivers on the Gold Coast have burst their banks, and there’s a flood warning for Maroochy and Mooloolah rivers on the Sunshine Coast.

Queensland Fire and Emergency Services co-ordinator Brian Cox urged people not to leave their homes and if they do to take extreme caution.

“Be really vigilant,” he told 4BC Radio.

“It will not take much with the current rainfall they’ve already experienced, and the saturation levels we’ve currently got across southeast Queensland, for any minor storm to hit, to raise those flood levels and water levels across roads and as you know that can be quite dangerous.”

-with AAP