"Life-threatening flash flooding" has been forecast for large parts of Victoria today as the state barely recovers from a hot, humid, and windy night that brought down transmission towers.

Key points: Six power transmission towers collapsed in strong winds near Cressy overnight

Six power transmission towers collapsed in strong winds near Cressy overnight At least 300 calls were made to the SES and about 20,000 properties were affected by blackouts across the state

At least 300 calls were made to the SES and about 20,000 properties were affected by blackouts across the state East Gippsland will experience very high fire danger but receive little to no rain

A cool change has swept through the west and central regions of the state including Melbourne.

Victoria's east has remained hot and dry with less than 5 millimetres of rain forecast for the rest of Saturday.

Temperatures in Melbourne have slowly dropped from a high of 29C this morning to 19C at 3:00pm.

Mud rain has begun to fall turning gutters a rusty red and causing isolated flash flooding but the risk of hail has decreased.

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The public are being warned to watch out for fallen trees and debris on the road and have been told to avoid driving through flood waters.

There is a severe thunderstorm warning for the Northern Country and parts of the Mallee and a severe weather warning is still in place for heavy rainfall and flash flooding expected to hit western and central Victoria.

A Bureau of Meteorology (BOM) spokesman said the highest rainfall recorded since 9:00am was 27mm in Trentham in the central district and 24.2mm in Charlton.

Intense rainfall is forecast to lead to "life-threatening flash flooding" with rainfall totals of between 20 millimetres and 50mm expected and isolated falls of up to 100mm possible in Horsham, Warrnambool, Seymour, Maryborough, Ballarat, Geelong, Melbourne, Wonthaggi and Bacchus Marsh.

The BOM has also warned rainfall and accompanying high humidity today could lead to a "heavy outbreak of brown rot" in stone fruit farms.

Fire threat to increase

Firefighters will be under pressure this afternoon and tonight with rain unlikely to fall in the dry and windy eastern parts of the state.

State Emergency Commissioner Andrew Crisp said there were 10 ongoing fires in the north-east and East Gippsland that had been burning since November last year.

An emergency warning was issued for a fire at Cape Conran in East Gippsland just after 1:30pm on Saturday.

Large plumes created by a wind change later today could see private property threatened.

A wind change later on Saturday could flare already burning fires and threaten communities.

Transmission towers topple in severe winds

Temperatures soared into the 40s yesterday with Avalon, near Geelong, registering 44.3 degrees Celsius at 2:50pm. Melbourne Airport registered 42.3C at the same time.

Six power transmission towers collapsed from a storm that hit Cressy near Geelong overnight. ( Facebook: Karen Saunders )

The humidity quickly rose and severe thunderstorms swept through Melbourne in the early evening, knocking down a significant number of trees, damaging homes and powerlines and causing traffic hazards primarily around Frankston but also Geelong, Horsham and Bendigo.

An SES spokesperson said about 700 incidents were reported statewide with 500 related to fallen trees.

An AusNet Services spokeswoman confirmed a storm yesterday afternoon north of Colac led to six transmission towers on the Moorabool to Mortlake and Moorabool to Tarrone transmission lines being knocked to the ground.

A further two towers suffered extensive damage.

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"It resulted in a separation between Victoria and South Australia at the Heywood Interconnector and an interruption to supply to the Portland aluminium smelter," she said.

Vic Emergency issued a warning this afternoon about downed power lines lying across a number of fences in Cressy, which could be electrified as a result.

People should stay at least 300 metres away from fallen power lines or transmission towers.

Extremely high power demand related to the heat and multiple generation outages caused problems for the energy network overnight, with more than 20,000 properties across the state affected by blackouts.

Supply to the Portland smelter, the biggest energy user in the state, was affected.

Elton John's show at Rochford Wines in the Yarra Valley was cancelled 95 minutes into his set after heavy rain struck the stage damaging musical instruments and monitors.

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Fire demolishes school building

Amid the high fire risk across the state, the roof of a building at Sandringham Primary School in Melbourne collapsed after a large fire early this morning.

Forty firefighters responded to the blaze which started shortly before 4:20am in Bamfield Street and was brought under control by 6:15am.

Firefighters responded to a fire at Sandringham Primary School this morning. ( Facebook: Brad Rowswell )

The fire threatened other buildings but it is not clear at this stage how it started.

Emergency officials on alert for fire risk

Steve Chircop, who lives at Smythesdale near Ballarat, was able to save his neighbours' home when a fire broke out during the hot weather.

Mr Chircop left work early because of the heat and was checking his dogs when he saw the grassfire.

"It went from the size of a small kids' pool to the full paddock in 30 seconds," he said.

"By the time I got off the phone to triple-0, it was going for kilometres. It was that quick."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 49 seconds 1 m 49 s Firefighters extinguish a tip fire at Clayton South

When the fire spread quickly towards a neighbour's home, Steve and other locals soaked the house with water from homemade carts.

Firefighters were able to slow the spread of the fire and authorities downgraded their warning to advice level.

While the fire at Bendoc in East Gippsland was on Friday evening downgraded to watch and act, it had flared up earlier, triggering emergency warnings.

Andrew Nixon, a spokesman at the Orbost incident control centre, this morning said more than 100 Victorian firefighters were working on the fire plus personnel from nearby NSW.

"There's a lot of heavy smoke in the air this morning," he said.

"That may reduce our ability to have any air operations over the fire."

The fire is closest to Bendoc Upper where there are about half a dozen houses.

Mr Nixon said the fire is still about 12km east of the much larger community of Bendoc, which has more homes, a pub, general store and post office.

"We're pretty confident that if that fire does move to the west of Bendoc that we have the resources to deal with that," he said.