Hailstones the size of tennis and golf balls have damaged homes and thousands of cars around Sydney.

Images on social media showed dented cars, broken windshields and a hazardous, snow-like landscape during the Australian summer.

The Bureau of Meteorology called the bad weather which struck on Thursday evening the "worst hailstorm in 20 years".

Some hailstones that fell in western Sydney and its suburbs were five to eight centimetres in diameter.

The Insurance Council of Australia counted more than 25,000 claims on Friday, three-quarters of them for vehicle damage, and expected the number to grow sharply.

Mother shields baby daughter with her own body during freak hail storm in Queensland

New South Wales emergency services received hundreds of calls during the night.

Christopher Mawn, spokesperson for the state emergency services, said many involved homes where rooms were uninhabitable and ceilings had collapsed.