Torrential rain has prompted a weather bureau warning of flash flooding across eastern Sydney, including the CBD.

And what is being reported as a twister tore the roof off a garage in Macpherson Street, Bronte, about 11.25am, police said. Two people - a woman and a child were home at the time, but neither were injured.

Weatherzone.com.au meteorologist Martin Palmer said there were reports of a small spout but was impossible to record such events. He said that there was a very low risk that another spout would hit the east coast of Sydney within the next 12 hours. Weatherzone.com.au is owned by Fair fax Media.

The severe weather warning was issued shortly before 2pm today, with advice not to drive, cycle or walk through floodwaters.