Strong winds and heavy rainfall have downed trees, damaged properties and flooded roads as a complex weather system lashed Australia's east coast.
About 200 properties in Burrill Lake on the NSW south coast were flooded overnight, the State Emergency Services said.
Emergency crews responded to a surge in rescue incidents around Shoalhaven as flash flooding swept through the area with the majority of incidents overnight involved fallen trees, powerlines and damaged roofs.
More than 200mm of rain also smashed several towns including Morton and Ulladulla.
Communities stretching from Queensland's Lockyer Valley to Bega on NSW's south coast are still being warned to take care as severe weather driven by a "vigorous" coastal low lingers offshore.
The storm, called a cyclone bomb, was expected to track south on Wednesday before turning back out into the Tasman Sea on Thursday.
Heavy rainfall which may lead to flash flooding continues in the southeast and extending southwards towards Bega and inland to Braidwood.
Isolated totals up to 120mm are expected but conditions are expected to ease later in the day.There are 29 warnings current, with residents in Sanctuary Point being told to move to higher ground.
NSW SES crews had responded to more than 2320 incidents by early Wednesday morning, as the low shifted southwards from Newcastle toward Sydney, the Illawarra and South Coast.
More than 17,000 homes and businesses from western Sydney down to the Illawarra are without power, Endeavour Energy said, and several flights are cancelled from Sydney Airport for the second consecutive day.
Residents were being warned to evacuate amid coastal erosion on the Central Coast. Dunleith Tourist Park manager Ryan Lloyd told AAP the beaches were heavily affected as wind gusts and swells intensified.
"It's pretty wild - pretty full on - a bit scary for the home-owners too," he said.
There were patches of blue in the sky but they were otherwise surrounded by dark clouds.
"It's quite ominous, quite eerie."
But the rain was less of a concern than the strong winds.
"We've already had plenty of tree branches down ... they're dropping limbs everywhere," Mr Lloyd said.
"It's just battening down now, just wait for it to blow over - pardon the pun - then a massive clean-up for the next couple of days."
The Bureau of Meteorology is predicting another low-pressure system to enter the storm's path later on Wednesday.
"We see another low-pressure system, really dumb-belling around that first one, that will really intensify and reinforce some of those winds and rain across the south coast," senior meteorologist Jonathan How said.
The system extends about five kilometres into the sky, with two low pressure systems interacting with one another in a phenomenon known to meteorologists as the Fujiwhara effect.
"It is very rare to see two east coast lows spiralling around each other like this," University of Melbourne associate professor and weather phenomena expert Andrew Dowdy said.