Newcastle lord mayor Nuatali Nelmes said council officials would inspect the area with a coastal engineer on Monday morning and the council would "need to look at relocation options" for a section of the park that includes six cabins on the shore.

Guests in two cabins were moved to other parts of the caravan park. The others were empty, while guests in other areas were unaffected.

City of Newcastle owns the park and a private operator manages it.

Cr Nelmes said the park had "not fared well with the loss of some of our erosion markers and the erosion escarpment within 5.5 metres of the footings [of cabins on the shore]."

"Inspections have been undertaken throughout the day," she said.

Deborah Holland, a spokeswoman for the caravan park, said: "We're not putting guests in those six as a precautionary measure while we assess the situation and keep an eye on the weather".

"A further judgement call will be made on Monday, regarding any further issues with the beach and tides."

While the full extent of erosion at the caravan park had not been determined on Sunday, it is believed the effects would have been worse without the council's sandbagging work.

"We are being told that the sand nourishment project from last year has had some impact in reducing shoreline recession," Cr Nelmes said.

Cr Nelmes said the northern end of the surf's club's seawall and the southern end of the Mitchell Street seawall had also been affected

"We will continue to monitor the situation closely and assess what actions need to be undertaken."

Meanwhile, a teenager was dramatically rescued after falling from his canoe in the Allyn River in the Dungog-Lower Barrington area.

"The SES and Port Stephens-Hunter police have rescued a 16-year-old boy who was trapped between debris in waist-deep water after falling into the Allyn River about 9am," NSW deputy state emergency operations controller Karen Webb said.

"The teen was in the water for almost two hours before specialist SES officers were able to free him and safely return him to the riverbank. He's since been taken to hospital with suspected broken ribs."

The teenager was trapped against timber in the river and had to be freed by an NSW SES Swiftwater Rescue technician.

He was hauled to safety by the combined rescue teams. All those involved are now safe.

Ms Webb said Brisbane Water police on the Central Coast and residents had "put their lives at risk to rescue five men whose fishing boat capsized as they tried to navigate in the dark to go fishing" on Saturday night.

"The water conditions were so dangerous that Marine Area Command were unable to assist, yet none of the men were wearing life jackets and struggled to swim," she said.

She was disappointed that she had to remind people to act responsibly and "not take risks in these types of conditions, especially when around floodwaters".

"We are investigating after a video surfaced online [on Saturday] of a man jet skiing in floodwaters on the Central Coast, which is behaviour so reckless I can barely comprehend it."

As torrential rain hit the Hunter Region on Sunday morning, the Bureau of Meteorology warned of the risk of "life-threatening flash flooding".

The bureau issued a severe weather warning for the Hunter, amid torrential rain, high winds, large waves and "abnormally high tides".

Steven Lawrence, a spokesman for SES headquarters at Metford, said 233 calls for assistance were received in the Hunter from midnight on Saturday to about 5pm on Sunday.

Of these, 191 were completed by around 5pm, with only 42 outstanding.

Mr Lawrence praised SES volunteers for doing a great job. He said 40 teams of four had been in the field.

Some of the worst-affected areas were Rutherford, Nelson Bay, Maitland, Adamstown, Raymond Terrace, Swansea, Gillieston Heights, Singleton and Wallsend.

The type of damage included leaking roofs and trees down on properties.

Mr Lawrence urged people not to drive through floodwaters in the Hunter.

"A strong message we're trying to get out there is please don't drive, walk or ride through floodwaters," he said.

"You're putting your own life, volunteers and rescuers at risk. There's an awful lot of water on roads and some roads have been closed. A number of causeways have water over them."

In the 24 hours to 9am on Sunday, Nelson Bay received 102 millimetres of rain, University of Newcastle 75 millimetres, Lake Macquarie 84 millimetres and Williamtown 66 millimetres.

Maitland Airport copped 66 millimetres, Nobbys Head 50 millimetres, Scone 32 millimetres and Murrurundi 29 millimetres.

From 9am to 5pm on Sunday, Nobbys recorded 19 millimetres, Gosford 90 millimetres, Norah Head 56 millimetres, Williamtown 13 millimetres, Cessnock 13 millimetres, Maitland 16 millimetres and Tocal 17 millimetres.

Maryville in Newcastle was among the places to experience intense rain on Sunday.

Water lapped at Sue Russell's property at the corner of McMichael Street and The Avenue.

"I was out at about 7am and the street was already flooded. By the time I came back by 10am, it was probably the highest I'd seen it. I've been here close to 10 years," she said.

On Sunday at 4pm, the Bureau of Meteorology issued a "flood watch" for catchments in the Hunter.

A coastal trough off the NSW coast was being "monitored for east coast low development over the next 24 hours".

"This system will move only slowly southwards through Sunday and Monday and bring increasingly widespread and prolonged periods of rain to the Hunter and southern NSW coast," a statement said.

"High tides forecast on Sunday through to Tuesday may exacerbate flood conditions in low lying coastal areas."

Catchments likely to be affected include Karuah River, Wollombi Brook and Lower Hunter River, Newcastle area, Paterson and Williams Rivers, Lake Macquarie and the Central Coast.

The flood watch means that people living or working along rivers and streams must monitor the latest weather forecasts and warnings and be ready to move to higher ground should flooding develop.

Flood warnings will be issued if minor flood levels are expected to be exceeded at key sites along the main rivers.

The SES urged people to closely monitor the situation and plan ahead around possible road closures and inundation of low-lying areas if lake levels continue to rise.

It warned people to stay out of rising water; seek refuge in the highest available place and move vehicles under cover and away from areas likely to flood.