Scorching weather has brought blackouts, bushfires and tropical humidity to Victoria amid warnings of more wild weather to come including a possible repeat of last week's hail, mud rain and flash flooding.

Key points: Victorians have been urged to set their air conditioners to between 23C and 26C to reduce strain on the electricity grid

Victorians have been urged to set their air conditioners to between 23C and 26C to reduce strain on the electricity grid Warnings are in place for fires, dust storms and thunderstorms

Warnings are in place for fires, dust storms and thunderstorms Temperatures above 42C recorded in Melbourne and Geelong

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

Late in the evening, a fire burning at Cape Conran in East Gippsland was downgraded from emergency to watch and act level — with fires at Wulgulmerang and Bendoc also at watch and act.

Continuing the string of puzzling weather, severe thunderstorms swept through early evening knocked down a significant number of trees, damaging homes and powerlines and causing traffic hazards primarily around Frankston but also Horsham and Bendigo.

An SES spokesperson said about 300 incidents were reported statewide.

Meanwhile, more than 20,000 properties across the state have been affected by blackouts.

Victorians were asked to reduce their energy usage until about 8:00pm by avoiding using appliances such as dishwashers and washing machines and temporarily switching off pool pumps.

The Australian Energy Market Operator (AEMO) said damage to multiple transmission towers in western Victoria, extremely high demand related to the heat, and multiple generation outages were causing problems for the energy network.

"The loss of additional generation capacity or transmission outages in either state, may result in the need for rotational load-shedding across both Victoria and NSW," a statement said.

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

On the positive side, a predicted dust storm has so far failed to materialise, with Melbourne's air quality this evening rated as "good".

People escape the heat at Geelong's Eastern Beach. ( ABC News: Nicole Mills )

More weird weather

Bureau of Meteorology state manager Andrew Tupper warned that on Saturday Melbourne could see a repeat of last week's bizarre weather.

With the wind bringing dust from the north-west, the city could see more mud rain, though it might not be as bad as last time, and there could be some patchy rain heavy enough to cause localised flash flooding.

"The odds are if we get severe storms tomorrow there will be hail," he added.

"Most likely the hail will be less than 5 centimetres [in diameter] which is still a pretty decent size, but it's less likely that we'll see the giant hail that was observed in some places."

Hail is expected to fall in some areas, but the stones are unlikely to be as big as those that fell earlier in January. ( Twitter: @_Kaelon_ )

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."

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.

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 this afternoon and the previous night.

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 12 kilometres 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.

Elsewhere around the state, an emergency warning was issued at 6:35pm for a grassfire at Ingliston, Myrniong and Pentland Hills near Bacchus Marsh however it was downgraded to advice level about an hour later.

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

And in the city on Friday, the Metropolitan Fire Brigade was called to a fire at a tip facility in Deals Road at Clayton South.

An MFB statement said firefighters brought the fire under control at 2:55pm

The humidity is forecast to build to oppressive levels, the Bureau of Meteorology said. ( ABC News: Patrick Rocca )

Health warnings about humidity

Loading

Health authorities have been urging Victorians to take care in the very hot weather as the humidity increases.

Members of the construction union working on high-rise buildings in Melbourne were sent home before noon when the temperature hit 35C.

Diana Eadie from the Bureau of Meteorology said the humidity would become oppressive on Friday night and into Saturday morning.

"It's going to feel in some parts more like a build-up day in Darwin rather than what we're accustomed to in Melbourne," she said.

Ambulance Victoria's director of emergency management Justin Dunlop said by following some simple advice everyone will get through the day safely.

He said it was important for people to check on elderly relatives and neighbours who may be heat-affected.

"Our message to everyone out in Victoria today is to plan your day, try to stay out of the heat, carry a water bottle," he said.

Department of Transport spokesman Andrew Crook says even a few minutes in a hot car could be very dangerous.

"Never leave children or pets unattended in parked cars as those temperatures rise quickly to dangerous levels and just a few minutes can have tragic consequences," he said.