Australia's biggest city Sydney was smashed by a tornado-like storm on Wednesday, with hail as big as golf balls and winds gusting at 200 kilometres (124 miles) an hour causing havoc.

Two people required treatment -- one for shock and one for a head wound -- in the hardest-hit suburb of Kurnell, an ambulance official said.

One resident of the suburb, where wind gusts of 213 kilometres per hour were recorded, said the storm sounded "like a freight train going through".

"Total destruction," he told Sky News of the aftermath of the tempest, which downed trees and power lines and damaged buildings, including a desalination plant, and flooded roads.

Another man who called in to Sydney talk radio described a scene of extreme damage in Kurnell, images of which showed a truck overturned and building parts flung around.
"My neighbour's roof is gone, the trees are all down in the front yard," he told the Australian Broadcasting Corporation.

"There's trees down out the front of his house which have landed in my front yard. It's just a mess."

The weather bureau said warnings for destructive winds, large hail stones and heavy rain were in place for central Sydney, its airport and the Sydney Harbour Bridge.

"Very destructive winds associated with a possible tornado affected the Sydney coast around Kurnell at 10:30 this morning," the bureau said of the earlier lashing.

"We don't get situations like that without it being a tornado," the bureau's Michael Logan added.

"It is what's called a supercell thunderstorm and they're one of the most dangerous thunderstorms we get."

The bureau said surrounding areas to the north and west of Sydney were in line to be affected as the storm, which comes at the start of the southern hemisphere summer, moves north.

The airport remained open, but delays were expected as ground crews struggled to cope with the weather, a spokeswoman said.