Rainwater flooded homes in inner Sydney and seeped through roofs in Wollongong after three consecutive days of heavy rainfall across the central NSW coast.
At least two tornadoes were reported across the state, including one captured on camera from a fire tower at Young as it tore through a field in NSW's southwestern slopes region.
The rain continued into Thursday, with Newport on Sydney's Northern Beaches recording 122mm of rain in the day to 9am and Cronulla notching 147mm.
It made this month one of Sydney's wettest Septembers on record.
Multiple severe weather warnings remain in place, including alerts for damaging winds and hazardous surf across NSW.
The State Emergency Service has received more than 850 calls in 24 hours, mostly due to heavy rain.
During 50 minutes on Wednesday, the service received a surge of calls from across Sydney from those stranded in their homes or trapped in vehicles on flooded roads.
A group of hikers was rescued at Wattamolla, south of Sydney, after heavy rainfall hit from 1pm on Wednesday.
Reprieve is on the horizon as conditions are expected to ease on Thursday.
But several warnings remain in place.
Parts of the Hunter, Mid North Coast and Northern Tablelands are on alert for damaging winds.
Gusts with peak speeds of 90km/h are expected to last into the afternoon due to a complex low-pressure system, the Bureau of Meteorology says.
Meanwhile, a hazardous surf warning has been issued for Macquarie Coast, Hunter Coast, Sydney Coast, Illawarra Coast and Batemans Coast.
Large and powerful south-to-southeast waves are forecast to batter the northern and central coasts through to early Friday, bringing hazardous surf and increased risk of damaging waves and coastal erosion.
NSW Police Marine Area Command has advised people to consider staying out of the water and avoid walking near surf-exposed areas.
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