A motorist trapped in a car has become the first fatality of floods on Australia's east coast.

The car was trapped in floodwater at dawn and emergency services recovered the car with a body inside on Wednesday afternoon, officials said.

While rain has eased across New South Wales state, the flooding emergency continued with rising river levels.

Prime Minister Scott Morrison expressed Parliament's condolences to the family of the man who died at Glenorie, 25 miles north west of Sydney.

He said: "This is a terribly sad day for that family.

"We have seen so much over the course of the past year and more as this country has battled so many things - floods, fires, viruses, drought and now these floods again."

Emergency services have made hundreds of rescues since the flood emergency in Australia's most populous state began last week.

A flotilla of boats was delivering crucial supplies to isolated communities on the flooded Hawkesbury River northwest of Sydney and ferrying stranded residents to safety.

Mr Morrison took a flight over the Hawkesbury to survey the damage early on Wednesday.

He said: "The expanse of water that went right across that region was quite devastating to see."

Cabinet minister Peter Dutton said more than 700 defence personnel would soon be deployed as the floods recede to help people return to their homes and businesses as quickly as possible.