Emergency crews say they have responded to more than 400 calls for help as wild weather continues to lash parts of Sydney.

Flash flooding closed roads across the city, while a three-car accident on Roseville Bridge caused long delays.

Sydney was also hit by its own mini tornado, which damaged 11 homes in the city's eastern suburbs after it came ashore just before midday AEST.

Homes in Garrett Street, Maroubra, have mostly minor damage such as holes in roofs and tiles being blown off.

The wet weather is expected to continue well into the night. SES crews are on standby for more flooding.

The Sydney twister comes a day after more than 30 homes were damaged in the north coast town of Lennox Head when a waterspout crossed the coast and became a tornado.

Andrew Haigh from the Bureau of Meteorology says the Sydney storm was not as bad.

"The one in Lennox Head yesterday - we call it a full-scale tornado," he said.

"That was clearly more intense than what we have in Sydney today.

"The clouds are a lot lower, there isn't as much instability but nevertheless it is always possible in these situations that with the updraught of a shower cloud you can get a rotation of the air underneath...and the formation of what we would call a waterspout or a very small tornado."

Mr Haigh says the tornado was too small to be picked up on radar screens, and would have even been hard to see with the naked eye.

"The fact that not many people have spotted this is probably due to it being hidden amongst a lot of heavy rain, so it wouldn't have been all that visible," he explained.

"But it does appear there has been a significant whirlwind type feature which we'll call a water spout if it's coming in off the water, and that has caused some damage."

The bureau issued a flood warning for Sydney's east as heavy rain continued to lash suburbs.

Paul Johnson from the New South Wales Fire Brigade says crews have had a busy day.

"From about 1.30pm we had hundreds of firefighters out attending various incidents such as flooding, trees down, we were pumping out flooding basements, houses were about to flood," he said.