A STRING of thunderstorms that swept across Sydney, the Blue Mountains, the central coast and the Hunter Valley yesterday caused flash flooding and hail the size of golf balls.

A family of four were rescued from their home in Hazelbrook after it was inundated with water from overflowing drains.

Another Hazelbrook resident, Lisa Maxwell, said she was left bruised and cut by hail as she tried to protect her car from the hail stones about 1pm. The bottom floor of her home was also flooded. ''I had a big golf umbrella but the hail was just so big it was hitting my arms,'' Ms Maxwell said.

There were also reports of small hailstones in Cronulla.

The State Emergency Service received close to 200 calls for assistance. An SES spokesman, Phil Campbell, said many of the calls were from householders with leaking roofs and water coming into their homes due to blocked and overflowing gutters.

''We also attended properties with trees and branches over driveways and fences,'' he said.

Mr Campbell said the family in Hazelbrook called for help after an intense downpour caused a torrent of water to flow down an embankment behind their home.