Victoria ran out of ambulances last night as wild weather triggered scores of cases of "thunderstorm asthma".

"It's a phenomenon we've only seen rarely before," Holman said.

"Within an hour (of the storm hitting) we'd received 160 calls, and had run out of resources."

"I can only speculate, but I think it was caused by the huge amount of irritants and pollens in the air."


"We've called on our colleagues at MFB, asking their Emergency Medical Response team to operate outside their normal parameters. And we've also called on Victoria Police to assist us."

Ambulance Victoria regional services general manager Mick Stephenson said paramedics attended to more patients in five hours yesterday than they usually assist in a whole day.

Stephenson said between 6pm-11pm, Victorian ambulances dealt with 1800 cases, many of which had respiratory issues from 'thunderstorm asthma".

"By and large, it looks to be respiratory cases, and certainly a strong rise in asthma cases last night; and we were seeing asthma in people who had never reported asthma previously, so it's the most unusual circumstance," Mr Stephenson told 3AW.

Mr Stephenson said more than 60 additional ambulances had to be deployed to deal with the unprecedented workload.

The demand continued to grow last night with 90 patients waiting to be seen by a paramedic at 10pm.

Earlier the storm lashed Melbourne's west, tearing off roofs, snapping trees in half and knocking air-conditioning units to the ground.

In bayside suburbs thousands lost power, hours after fireys were lucky to survive their truck being caught in a Swan Hill blaze.

The State Emergency Service (SES) has been bombarded with calls for help following the predicted storm that swept the state.

SES spokesman Marc Dorey said 350 calls had been made since 4pm, most reporting storm damage and fallen trees in Hobsons Bay and Wyndham areas.

Suburbs which were hit the hardest include Altona, Altona Meadows, Hoppers Crossing, Wyndham Vale, Werribee, Tarneit and Truganina.

Two people have been relocated for the night after a tree crashed through the roof of their Dunolly home near Bendigo.

The storm damage comes after the hottest November day in six years had the Bureau of Meteorology issue its very first fire weather warning of the season.

But the weather turned in the evening, with Lorne beach closed due to a lightning warning.

And in true Melbourne fashion, while Melburnians were scorched in the day, rain lashed the city by late afternoon, before the temperature tumbled in minutes from the mid-30s to the mid-20s.

The forecast is for just 17C today.