Australia Weather News

Witnesses saw a man being swept away after his vehicle went into floodwaters near Lismore in far north New South Wales, police say, as a heavy downpour and strong winds hit the state's coast.

Police were called after a man's vehicle was seen being swept from a concrete causeway into Leycester Creek at Larnook, between Lismore and Kyogle, about 3:00pm.

Police said witnesses saw the man climb from the vehicle and hold onto a nearby tree, before being swept downstream a short time later.

Police have since called off the search for the missing man due to dangerous conditions in fast-flowing waters, but are expected to resume searching on Thursday morning.

The Bureau of Meteorology (BoM) said a low pressure system that was developing off the Central Coast was behind the bad weather, which is also predicted to bring flash flooding.

In Sydney, the eastern suburbs and northern beaches were likely to be hit the hardest, with rainfall of up to 100 millimetres expected.

Other areas within the Sydney basin, including the city's western suburbs, are expected to get lesser rainfalls of 30 millimetres.

The conditions are expected to ease by Thursday morning as the low pressure system moves further east.

"We can't rule out falls in excess of a 100 millimetres right from Cronulla all the way up to the Central Coast," said the BoM's Robert Taggart.

He also warned motorists to be prepared to encounter flash flooding.

"It could affect traffic during peak hour and after peak hour," he said. "Particularly where there is heavy rainfall near the coast."

The SES said its volunteers were on standby across affected parts of the state.

Spokesman Phil Campbell said drivers who came across roads that were flooded needed to use common sense.

"It's really important to turn around and find a safer route," he said.

"It's much better to get home a little bit later than not to get there at all.