While the cool change has hit Melbourne, other areas across the state's north and east continue to swelter.

The temperature was still a scorching 46 degrees in Swan Hill just before 4.30pm, while Mangalore was sitting at 46.3, Castlemaine was still 43 degrees and Sale was hovering at 45.3 degrees.

"The heat is still very intense in the north and east of the state," Bureau of Meteorology senior forecaster Michael Efron said.

"Bendigo is still about 43.5 degrees while Bairnsdale is 45.5 but we expect a dramatic cool change to move through both those areas around 5 to 6pm."

Metro Trains have begun lifting speed restrictions around Melbourne, with delays set to subside across the network.

Trains are now able to lift their speeds above 70 km/h, meaning less services will be delayed or cancelled.

Currently only the Williamstown line faces major delays, with the Craigieburn line still suspended.

Yellow is solar, green is wind, brown is coal and the dark blue bit down the bottom is imported power.

Here's the view of Kevin Parkin, meteorologist at the Bureau of Meteorology:

"It’s been an extraordinary summer. It may not have felt like that in southern Victoria, but certainly across the rest of the state...The heatwaves we have had are almost unprecedented. Relentless days of 40-plus degrees, plus warm nights."

Here's a scary thought as well: the smoke column over the Timbarra fire in Gippsland produced its own lightning.

"It’s incredibly dangerous ... and it makes the fire pretty much impossible to fight. The concern is when the wind change hits that fire, the whole eastern flank will become the front of the fire and run up the valleys of East Gippsland."

The energy market operator says the power is back on for 200,000 households after a blackout it had to have to protect the grid.

"The interruptions, together with the emergency resources procured under the Reliability and Emergency Reserve Trader (RERT) mechanism in Victoria, were needed to protect the power system during record-breaking high temperatures, high demand and reduced generation availability," the Australian Energy Market Operator said.

Electricity distributors progressively shed power around designated suburbs, aiming to limit the cuts to between one hour and 90 minutes per area.

However, AEMO said there may still be some homes without power.

By 4pm on Friday more than 19,600 homes were still without power.

Powecor reported 13,702 power outages including 1433 houses in Caroline Springs and more than 900 customers in Caulfield North.

Citipower also reported 1615 customers and were still without power.

Jemena, which covers Melbourne's north and north-west, reported about 150 houses were without power including 139 in Williamstown and 12 in Moonee Ponds.

AusNet reported more than 3108 power outages, while United Energy reported 1018 customers were still without power.

Opposition leader Michael O'Brien has released this statement:

"Today’s rolling blackouts show up the failure of Daniel Andrews’ energy policies.

"Something is seriously wrong when the power goes out in Victoria because we don’t have enough supply.

"On a day of extreme temperatures, there are serious health and safety concerns with deliberately cutting off supply.

Lily D’Ambrosio, Victoria's Minister for Energy, Environment and Climate Change, is holding a press conference over the load shedding that left more than 100,000 customers without power during a heatwave.

"Despite initial reports this morning from the AEMO who advised we had more than sufficient power to meet all our needs, the situation changed very quickly," she said. 

"What happened is the extreme heat continued to remain with us, and demand continued to increase to unanticipated levels. Because of that, that caused greater stress on our existing thermal generators. Under that ongoing and increased stress, they were not able to continue to provide the power supply they were doing so up until then. It meant a reduction in power output from the existing generators.

"That came on top of the fact we’d lost three units of coal generation ... in the Latrobe valley. With those changing set of circumstances, the market operator did what the market operator's job is. It decided there was a gap to meet that continuously rising demand for energy. That gap was around about 250MW.

"In that context, we lost 1800MW of power capacity. That’s an extraordinary figure to lose power in Victoria. Essentially, most of that was as a result of failed infrastructure from our coal and gas units, in particular coal, and of course a decrease in the amount of power from those generators that did reamin in our system."