Warragamba Dam began to spill this morning as Sydney braces for another day of heavy rain.
Water NSW said the catchment began overflowing at 7.30am today and may continue to spill for some time.
Residents are being urged to stay away from waterways and flood plains, including the Hawkesbury and Nepean rivers.
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As of 8am today, a flood advice alert was issued for Wamban on the NSW South Coast after downpours of 150mm were recorded across the Moruya and Deua Rivers in the last 48 hours.
The SES has also issued minor flood warnings for Bega, Colo, North Richmond and Menangle.
"You should stay informed by monitoring warnings issued by NSW SES on their website and Facebook page, listening to your local radio station, and checking the latest weather information from the Bureau of Meteorology online," the SES said in an alert.
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The Bureau of Meteorology said the South Coast and Illawarra are forecast to receive more than 100mm of rain over the next 24 hours.
Sydney is expected to record a further 20mm today after recording downpours of 30mm overnight.
"An upper level low over the Central Tablelands is pushing an area of rain into the southeast coast," the BoM said in an update today.
"The rain will contract northwards out of the South Coast during the day, and off the Illawarra coast through the afternoon and evening."
The Bureau warned heavy rain may lead to flash flooding in northern parts of the South Coast, southern parts of the Illawarra, eastern parts of the Southern Tablelands and far north-eastern parts of the Snowy Mountains districts this morning and afternoon.
Areas that may be affected include Nowra, Batemans Bay, Moruya Heads, Ulladulla, Narooma and Araluen.
Overnight, the SES attended Dover Heights in Sydney's eastern suburbs after heavy rain caused a sinkhole to open up at a construction site on a residential street.
The SES is urging residents to take care as further rainfall is expected tonight.
