Sydney's Warragamba Dam is spilling over after reaching capacity following a flurry of heavy downpours across the state.
WaterNSW has confirmed the dam began spilling at 7.30am on Sunday following widespread rain across Sydney catchments.
The water reservoir last spilled after heavy rain on April 6, causing catastrophic damage to some homes near the catchment area.
The SES has issued minor flood warnings for the Hawkesbury River at North Richmond and the Colo River but does not expect any significant impact to properties in the area.
"There will possibly be low-lying flooding over roads but we're not expecting major impacts like there was the last spill," an SES spokeswoman told AAP.
Over the past 24 hours to 9am on Sunday, Sydney has recorded rainfall totals in excess of 30mm at Campbelltown (35.4mm) and Observatory Hill (31.2mm).
Heavy rain and significant runoff led to a 10-metre wide sink hole opening up in a residential street at Dover Heights in Sydney's east on Saturday night.
"We were on scene until 1 o'clock this morning, using sandbags and a retaining wall to divert water away from properties," NSW SES Waverley-Woollahra Deputy Unit Commander Anthia Kollaras said.
"The hole was quite big, and part of the road had washed away."
It was one of 273 incidents SES volunteers attended across the state in the 24 hours to 8am on Sunday.
The South Coast and Illawarra regions have been hardest hit by the wet weather, with 117.6mm of rain falling at Moruya Airport in the 24 hours to 9am.
A severe weather warning remains active for heavy rainfall across parts of the Illawarra, South Coast, Southern Tablelands and Snowy Mountains forecast districts.
The Bureau of Metrology is forecasting some communities are likely to cop 90mm to 110mm over a 24-hour span, possibly rising up to 140mm over the ranges.
Nowra, Batemans Bay, Moruya Heads, Ulladulla, Narooma and Araluen are all in the firing line.
The heavy rainfall could develop into flash flooding in the warning area on Sunday but conditions are expected to ease in the evening.
