Flooding in the New South Wales Hunter region has led to evacuations, rescues and hundreds of calls for help as forecasters warn of more heavy rain and flash flooding in Sydney.

Newcastle roads were turned into rivers of fast-moving water as emergency crews dealt with more than 1,400 requests for assistance, including 700 across the Hunter region.

Across the state, rescue crews carried out more than 20 rescues from flood waters.

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Six streets in Raymond Terrace have been ordered to evacuate, with the Hunter River expected to exceed minor flood levels in the area in the hours ahead.

After a day of relentless rain, the Wollombi Brook is also likely to peak this afternoon.

Overnight, residents were evacuated from low-lying parts of the flood-ravaged town of Dungog, where wild weather led to three deaths less than a year ago.

Several rivers reached their peak overnight and are now falling, including the Gloucester River, the Myall River at Bulahdelah and the Williams River at Dungog.

However, a major flood warning remains in place at Bulga and authorities warned five homes were at risk of flooding in the small community of Glen Martin, north of Newcastle, as the Williams River there continued to swell.

Several areas have been dramatically impacted. Photo: AAP

Bureau of Meteorology (BoM) duty forecaster Dimitry Danchuk said rainfall there had increased rapidly.

“Effectively this area went from minor to moderate flooding to moderate to major flooding,” Mr Danchuk said.

“Some easing trend is likely to happen late in the day during the afternoon and evening, as we expect this low to gradually contract to the north east.”

Dozens of roads around the Newcastle and Hunter region are cut and motorists have been advised to avoid all unnecessary travel.

A New South Wales State Emergency Service spokesman said the small town of Torryburn was isolated by floodwaters.

“This is probably the second or third time we’ve been isolated since the April storms when we lost our bridge,” said local resident Craig Gardiner.

Wes, a resident of the Newcastle suburb of Carrington, said he was surprised by just how much rain was falling.

“This is the worst it’s been since I’ve been here in a couple of years,” Wes said.

“April storms were as bad as this but we’ve got a high tide so water just can’t get away. When the tide drops it will probably come down a bit.”

Farm country in the Tuross and Bega Valleys in the state’s south remain inundated, water levels in that area are receding.

Emergency crews are braced for intense winds of up to 90 kilometres per hour in the Hunter.

Campers trapped by floodwaters

Meanwhile, concerns are growing for a group of campers stranded at an isolated camping ground in a national park on the New South Wales far south coast.

Emergency authorities said the 21 campers in the Deua National park, west of Moruya, were running out of food and water.

SES incident controller Ashley Sullivan said several attempts had been made to reach the group, but low cloud and high winds had forced the helicopter to return to base.

Low-lying properties have been inundated with floodwater. Photo: AAP

He said chopper crews were waiting for the weather to clear.

“[Rescuers] tried to fly in on numerous occasions using the Westpac Lifesaver helo [helicopter] out of Moruya,” he said.

“Unfortunately due to, I guess the cloud cover, being so low at the moment … we can’t actually fly up there either so we are attempting another flight today.”

There were no reports of injuries.

SES regional controller Greg Murphy said conditions should improve over the next few days.

“Around the mid-south coast and up into the highlands we are looking at a couple of days of sunshine. So I think the end of the week is looking a whole lot better than the front end of the week,” Mr Murphy said.

SES deputy commissioner Greg Newton said the majority of flood rescues involved people attempting to drive through floodwaters.

He said a pregnant woman was rescued from a property that was isolated by floods in the state’s south.

“That went very well. I believe she’s in hospital,” Mr Newton said.

“We’re also out and about looking for people, looking in areas where people may be at risk such as low-lying camp grounds.

“Many people are on holidays at the moment so may not be familiar with their area, so they need to take that extra care to be aware of what’s going on around them and be prepared to move if required.”