Emergency crews have rushed to 30 flood rescues in less than an hour as heavy downpours engulfed millions of residences along the east coast.

One of the many dozens of rescues included 30 passengers stuck on a light rail in Sydney, which was lashed with 120mm of rain.

Rainwater flooded homes in inner-city suburbs and seeped through roofs in Wollongong after three consecutive days of heavy falls 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 southwest.

The rain continued into Thursday, with Newport on Sydney's Northern Beaches recording 122mm in the day to 9am and Cronulla receiving 147mm.

It made September one of Sydney's wettest on record.

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