The Victoria State Emergency Service received more than 1500 calls for help in the 24 hours to 8.30am on Friday, with the most affected areas including Ballarat, Bendigo and Melbourne's eastern suburbs.
There were 1100 reports of trees down and 216 reports of building damage, and those numbers are expected to rise as damaging winds continue.
More than 500,000 households are without power.
Powercor and Citipower in the state's west have 183,000 customers off power with Bendigo, Ballarat, Geelong and Terang badly hit, on the Mornington Peninsula.
United Energy has 155,000 households out, Jemena in Melbourne has 50,000 customers missing power, and in the east of the state more than 128,000 Ausnet customers are suffering blackouts.
One caller told ABC Radio Melbourne she had never seen anything like the storms that hit Red Hill on the Mornington Peninsula.
"I've never seen so many trees down, trees ripped out of the ground, there's just mess absolutely everywhere," she said.
Most metropolitan and regional train services have been suspended and dozens of major roads have lanes closed, including the Eastern, Western and Hume Freeways, and the Western Ring Road.
Trees are down on roads across the state, traffic lights are have stopped working in numerous places, and the Department of Transport has urged people to avoid driving if they can.
"With high winds expected to continue this morning, drivers should be vigilant on the roads and ensure nothing distracts their focus from the road. Deferring your travel may be the best option," it said.
If people must drive, they should travel with care through all intersections, and if they encounter fallen power lines they should stay clear and call triple zero.
Several vaccination centres have been closed due to the storms, and there are reports VCE students have been unable to travel to their end-of-year exams.
The Bureau of Meteorology has issued a severe weather warning for damaging winds across much of the state on Friday, with speeds averaging 60 to 70 km/h and peak gusts of 100 km/h expected to develop along western and central Victorian coasts during the morning.
The winds will pass through Melbourne then extend to Gippsland in the middle of the day.
The highest wind gusts reported so far include 143 km/h at Mt William in the Grampians, 119 km/h at Melbourne Airport and 115 km/h at St Kilda.
More than 4000 lightning strikes were detected within a 400km radius of Maryborough, about 168km northwest of Melbourne.
The storm also caused widespread damage in South Australia, leaving more than 30,000 homes and businesses in Adelaide without power.
The state's emergency service is responding to 178 calls for help, mostly involving downed trees.