A group of children has been rescued from a bus after it became stuck in floodwater as torrential rain, flooding and gale-force winds continue to batter the NSW coastal region. 

State Emergency Services have been swamped with calls for help as heavy rain triggered flash floods in Sydney and Newcastle.

More heavy rainfall and damaging winds have been forecast for Monday morning, with drivers being urged to exercise additional caution on roads.

The severe weather comes as entire roads in south-east Queensland were inundated by more than 100mm of rain.

Several cars were cut off by rising floodwater and at least one driver had to be pulled to safety at the weekend.

The slippery conditions caused another car to roll over as Brisbane experienced the highest July daily rainfall total in more than 20 years.

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The wild weather quickly moved to parts of New South Wales. The SES made eight flood rescues in Newcastle, with people trapped in houses and cars.

Volunteers rescued nine children and the driver using an inflatable boat on Sunday afternoon.

Emergency workers were called to the bus at the University of Newcastle about 5.30pm.

A total of 74mm of rain had been recorded in the area in the two hours before, according to the Bureau of Meteorology.

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The organisation said on Sunday afternoon it was experiencing a high volume of calls for help in Newcastle and surrounding areas.

A severe weather warning was issued for the NSW coast from the southern border to Newcastle on Sunday night.

The BOM warned of heavy rainfall, damaging winds with gusts over 90km/h, and very heavy surf.

The NSW SES has been inundated with requests for help. Photo: ABC

A low-pressure system off the Hunter coast was expected to batter the Hunter and Sydney regions overnight, moving south on Monday morning.

The rain could potentially cause local and minor flooding along coastal rivers from Sydney to Moruya, and in the Snowy River, the bureau warned.

-with AAP