Heavy rain, strong winds in NSW Hunter

A town in the NSW Hunter region has had 112mm of rain in one hour as cyclonic conditions continue to batter the state.

Severe thunderstorms are hitting Maitland, Raymond Terrace, Cessnock and waters off Port Stephens, the BoM advised just before midday on Tuesday.

People in the area are being warned the heavy rain may lead to flash flooding.

SES deputy commissioner Steven Pearce stressed that people must not drive through floodwaters.

"This is going to be catastrophic today," he told Macquarie Radio.

The SES has received more than 4500 requests for assistance, he said.

He said an enormous geographic area was being affected by the cyclonic conditions.

Residents in low-lying parts of Newcastle may also be significantly impacted from the heavy rainfall on Tuesday afternoon.

In the hour to 9.45am on Tuesday, Tocal in the Hunter region, recorded 112mm of rain.

In the 24 hours to 9am, Dungog had received 312mm of rain, its heaviest recorded rainfall in more than 100 years.

Crawford (near Bulahdelah) had recorded 259mm, Wallsend 186mm, and Wahroonga 172mm.

The severe weather warning remains current for the Hunter, Sydney Metropolitan and Illawarra districts.

Strong winds at speeds of up to 100km/h are also affecting the Hunter region and parts of Sydney.

There is also a warning to sheep graziers in the Illawarra, Southern Tablelands, Central Tablelands and Hunter districts.