ABOUT 500 people have been isolated by flood waters in northern NSW.
It comes as people in the south of the state are told to prepare for 100km/h winds and flash flooding on Monday.
More than 200 calls for assistance were made to the NSW State Emergency Service (SES) on Sunday, as ex-tropical cyclone Oswald moved across the Queensland border, packing damaging winds and heavy rain.
Winds of up to 140km/h hit parts of the northern rivers, while in the northern NSW town of Darkwood on the Bellinger River around 500 people are believed to be isolated by floodwaters.
But while residents have been told to stock up, SES spokeswoman Jessica Chan said there were no fears for their safety.
"The community is quite used to it," she told AAP.
While 53 swift water rescue technicians were moved to the north of the state today to bolster local resources, Ms Chan said the SES would also be focussing their efforts south on Monday as Oswald moves south.
"We expect conditions in the north to ease after lunchtime on Monday, with that weather front increases to Sydney.
"We are expecting heavy rainfall and flash flooding."
A severe weather warning was issued for much of the state on Sunday, with the Bureau of Meteorology warning that gusts of 100 km/h are forecast for the mid North Coast, the Northern Tablelands, the metropolitan and Hunter during Monday.
"Beach conditions in these areas will be dangerous and people should stay well away from the surf and surf exposed areas," the BoM said.
Heavy rain which may lead to flash flooding is also forecast to extend to the Hunter overnight and to the metropolitan, Central Tablelands and Illawarra districts by tomorrow afternoon.
But BoM regional director Barry Hanstrum said the low-pressure system will move rapidly and should pass out to sea in the early hours of Tuesday morning.
"The rain and wind will ease from most of NSW on Tuesday as the low moves further offshore and into the Tasman Sea, but dangerous surf will continue into Wednesday," he said in a statement.
The NSW SES urged people returning to NSW's southern cities to be careful.
"With damaging winds and heavy rain expected in Sydney, Newcastle and the Central Coast on Monday, holiday makers should exercise patience, drive to the conditions and never enter flood water," NSW SES Commissioner Murray Kear said.