Flooding in NSW has caused evacuations, rescues and hundreds of calls for assistance with the Hunter region taking the biggest hit.

The Bureau of Meteorology (BoM) said the urgent threat of severe weather had subsided, with conditions easing across the state.

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Emergency crews dealt with 2,000 requests for assistance in Newcastle, with 800 of those in the Hunter region.

A man has been lost overboard off a yacht north of Newcastle, with emergency services conducting a search and rescue. Dozens of roads across Newcastle and Hunter have been cut with motorists urged to avoid unnecessary travel.

Rescue crews undertook over 28 flood rescues across the state, with flash flooding occurring in Sydney. BoM said the rainfall broke weather records and the storm-affected areas are expected to ease on Thursday.

Meanwhile, a group of stranded campers on the New South Wales far south coast remain isolated overnight.

Here is a breakdown of the damage, region by region.

Newcastle-Hunter

Dozens of houses evacuated and shops forced to closed as the Williams River flooded around Raymond Terrace.

Motorists urged to avoid non-essential travel and rail lines shut down.

Central Coast

Roads and bridges closed and caravan parks put on notice as water levels rose.

South Coast

A heavily pregnant woman airlifted to hospital and at least 21 campers stranded at a Bendethera Valley campground by rising floodwaters.

Mid-North Coast

Man missing after being thrown off yacht in rough seas near Broughton Island.

Sydney

Inner city streets flooded and some suburbs battered with more than 100mm of rain in less than 24 hours.

Greater Sydney

Some residents around the Colo, Hawkesbury and Macdonald Rivers left stranded after rising water levels forced the closure of key arterial roads.

By the numbers

* More than 200mm fell in less than 24 hours along parts of the mid-north coast.

* Newcastle recorded its wettest ever January day, receiving about 238mm of rain.

* Frenchs Forest on Sydney’s north shore received 129mm of rain in the past 24 hours.

* The SES received more than 2000 calls for help, particularly in the Hunter and Central coast.

-with AAP and ABC