Key Points

Heavy rainfall on Wednesday continued for a fourth consecutive day in regions over 100 km north of Sydney, exacerbating widespread flash flooding.

The NSW State Emergency Service (SES) said that it responded to 887 calls for assistance, including 118 flood rescues, in the 24 hours to Wednesday morning.

Around 16,000 people or 7,400 dwellings in the worst-affected areas could expect to be isolated for at least a day, Australian Broadcasting Corporation (ABC) quoted SES spokesperson Andrew Edmunds as saying on Wednesday morning.

SES was aware of 52 people trapped on tables, verandahs and their roofs, he added.

Local power provider Essential Energy has reported about 3,700 homes and businesses, mostly in Taree, Wingham, Tinonee, Burrell Creek, Hillville and surrounds are without power. "Crews will be out again today, assessing damage and completing repairs where it is safe to do so", it said in a statement on Wednesday.

Almost 100 schools in the affected areas were closed on Wednesday.

NSW Emergency Services Minister Jihad Dib told Radio National Breakfast this morning that he has asked for federal support and said the Australian Defence Force is due to arrive soon to assist with rescues.

SES Assistant Commissioner Colin Malone said in a statement that authorities were deploying "every available asset" to assist with rescues, Xinhua news agency reported.

"We've also had a large number of calls for help that we are still assessing how best to access those locations," he said.

"We've advised those people needing assistance to move to higher ground, as we're unable to currently access by boat, road or air due to the current weather conditions."

A severe weather alert from the Bureau of Meteorology (BoM) said that some parts of the Hunter, Mid North Coast, Northern Tablelands and Northern Rivers regions recorded 20-hour rainfall totals exceeding 200 mm.

It said that heavy rainfall is expected to continue through Wednesday and into Thursday for large parts of the state and could lead to "life-threatening" flooding.

Senior BOM forecaster Dean Narramore told ABC television that some areas received up to 500 mm of rain in 48 hours.

The water level in the Manning River at the Mid North Coast town of Taree, 250 km northeast of Sydney, on Wednesday morning surpassed the record-high set in 1929.

Evacuation orders have been issued for residents in eight towns, and residents of three more towns, including Taree, have been told that it is too late to leave.

Malone said that most of the rescues for people in trapped homes were being conducted in areas that were advised to evacuate on Tuesday.

- IANS