There have been more than 20 flood rescues in northern NSW, with at least one person taken to hospital after being rescued from their flood-stricken vehicle, as heavy rain continues to fall.

The NSW State Emergency Service said it responded to more than 350 calls for help overnight on Sunday.

Most of those came from the state’s northern region, with 60 from Sydney relating to fallen trees, blocked roads and property damage.

Days of rain lie ahead for parts of eastern NSW, with significant flood impacts, damaging winds and large waves.

On Monday, a severe weather warning for heavy rainfall and damaging winds stretched from the NSW mid-north coast at Kempsey to the central coast.

Newcastle residents were sandbagging as parts of the city flooded on Monday afternoon. There was also sandbagging in towns north of the city, including Raymond Terrace.

The weather bureau has warned isolated falls of up to 120 millimetres over six hours are possible across much of the region, leading to more flood watch warnings.

“We’re already seeing those coastal catchments respond quite quickly to rainfall over the weekend,” NSW SES operational media coordinator Emily Barton said.

“With the forecast heavy rainfall over the next few days, we’re anticipating renewed rises and many catchments to reach minor to moderate flooding.

“SES has pre-positioned flood rescue teams, high clearance vehicles and aviation assets throughout the high-risk areas, but we’re urging the community to stay alert.”

The SES has advised residents to be prepared to be isolated to for up to two days, as rain continues to fall.

BoM senior meteorologist Angus Hines said a band of rain that formed overnight into Monday was shifting north to the central and northern coastal regions.

The worst of the rain is expected on Monday and perhaps Tuesday.

Hines called the extended nature of the wet weather “significant”, saying days of rain was expected.

“Even though the daily rainfall totals aren’t super alarming, having that much rain three or four days in a row can lead to significant flood impacts, road closures and potential for some inundation of homes or properties or businesses,” he said.

Hines said the regions with the highest risk of damaging winds were the central, Hunter and mid-north coasts, along with parts of the central and northern ranges.

Hines said the regions with the highest risk of damaging winds and heavy rainfall were the central, Hunter and mid-north coasts, along with parts of the central and northern ranges.

Dangerous beach conditions are also possible from Sydney’s southern beaches to Seal Rocks with waves up to five metres possible.

A damaging surf warning has been issued for the coastline stretching from Gosford to Coffs Harbour.

Wyee, on the central coast, had NSW’s highest rain total between 9am Sunday and 6am Monday with 121 millimetres. Nearby, Dora Creek had 117 millimetres.

Season’s wintry freeze

Elsewhere, much of south-eastern Australia endured an early taste of winter with below-zero temperatures on Sunday night.

Forecaster Weatherzone said the chill was due to clear skies and dry air in a southerly airstream after a cold front at the weekend that then settled in the Tasman Sea.

The temperature at Melbourne Airport fell to exactly zero early on Monday morning – the site’s lowest May night on record, Weatherzone said.

“Temperatures were even more frigid on Melbourne’s north-eastern outskirts. The mercury in the Yarra Valley town of Coldstream plummeted below zero shortly after 10pm and stayed there until after 9am. The low of -5.3 degrees shattered the old May record of -3.7 degrees (records since 1994).”

In Melbourne itself, the temperature got as low as 2 degrees, the city’s chilliest night in four years.

On Tasmania’s east coast, the small town of Fingal fell to -8 degrees.

“While this fell just short of the town’s May record of -8.1 degrees, it was the coldest temperature recorded anywhere in Australia since July last year,” Weatherzone said.

Sydney wasn’t particularly cold, with an overnight minimum of 12.8 degrees amid rain and showers. But that followed its coldest maximum of the year so far on Sunday, with a high of just 16.4.

In South Australia, the coldest temperatures were in the south-east, with -4.5 degrees at Padthaway breaking the former May minimum record by more than a degree.

“The nearby town of Keith shivered through a low of -4.1 degrees, which was also a May record, while Coonawarra’s minimum of -3.5 degrees was the coldest May reading in 60 years of records,” Weatherzone said.

Adelaide’s minimum of 3.1 degrees was its coldest May night in 19 years.

More cold, frosty nights are likely across the south-east this week.

-with AAP