Wild storms packing hailstones the size of lemons and strong winds have battered Melbourne during a severe thunderstorm.
Roads have been flooded and some flights have been grounded at Melbourne airport.
The tornado hit Fiskville, 15 kilometres west of Bacchus Marsh, with reports its force picked cars up off the ground.
It is believed another tornado also struck Melton, which was one of the worst hit areas.
The weather bureau's Richard Russell says there was a tornado threat for about 20 minutes.
"The report we had was from a very credible storm spotter," he told ABC News 24.
"He reported that a car was blown off or across the road as it went through."
Victoria's emergency services have already received hundreds of calls for help with reports of hailstones the size of lemons and roofs caving in from heavy rain.
Spokesman Lachlan Quick says some highways are flooded and trees have fallen onto roads.
"Anecedotally, we've had reports of lots of lots of vehicles with front and back vehicles smashed," he said.
Some international and domestic flights have also been delayed.
Melbourne Airport's Anna Gillot says when the initial storm hit, flights were grounded but some have now resumed.
She is advising passengers to check departure times with airlines.
"We'll do the best that we can, it's just dependent on the weather and they're fairly horrific storms," she said.
"We're doing the best that we can and just ask people to be patient and take safety precautions."
The thunderstorms are moving east with flash flooding and more hail expected.
Duty forecaster Chris Godfred said earlier in the evening that on top of the severe storm warning for metropolitan Melbourne, there was also a general warning for the entire state.
"That ranges right up to the northern parts of country Victoria and across to the Wimmera and also extending down into western and central Gippsland," he said.
"The warning area does cover about 70 per cent of the state."
© ABC 2011
11:07 EST The Bureau of Meteorology is predicting that the next three months will be wetter than normal for most of Australia, with warmer nights for many regions.