Hundreds of people have been rescued amid flooding in New South Wales, Australia.

Authorities said 152 people had been rescued after torrential rains sparked warnings for residents to move to higher ground.

They said 72 rescues were undertaken in Sydney, Australia's largest city, where there were hazardous deluges in several of the state capital's low-lying suburbs.

Officials had said Warragamba Dam, which supplies 80% of Sydney's water supply and was at around 96% of capacity, could spill over on Monday - but there were reports the rain had caused it to spill two days earlier than expected.

Some roads in New South Wales were completely submerged. Pic: AP

Around 15 emergency evacuation orders were in place across the state, according to the New South Wales State Emergency Service.

The service said it fielded 4,128 calls for help in one 24-hour period.

Almost a month's worth of rainfall hit Sydney and the surrounding areas in the space of 24 hours. Pic: AP

One woman was rescued after her car became stranded in the water. Pic: AP

"Flood levels in some of the rivers, particularly in western Sydney, are continuing to rise," state premier Chris Minns told a press conference.

Downpours hammered the southeastern state throughout Friday, with almost a month's worth of rain hitting Sydney.

Cars were submerged in water. Pic: AP

Several of Sydney's low-lying suburbs were hit by dangerous flooding. Pic: AP

Warnings were issued telling people to avoid non-essential travel and stay indoors.

Sydney had 4.4 inches of rain over the 24 hours to Friday morning, according to data from the nation's weather forecaster, just shy of average April rainfall of 4.7 inches.