Victoria's energy supply is waning as the state swelters through extreme heat and another power generator is expected to fail.
The Australian Energy Market Operator confirmed on Friday it had asked electricity distributors to "load shed" through the afternoon.
It means that up to 30,000 residential and business properties at a time will experience brownouts to free up 100MW of power.
"It's all because, you know, we're balancing the weather, additional heat is stressing the generators," AEMO chief executive Audrey Zibelman said.
"We have one generator who has had some problems and they have been really struggling to stay on, but they're having to reduce to protect the machinery.
"Other generators are also struggling, simply because of the heat. So, it's all that in combination is what we're confronted with this afternoon."
Three generators, two at Yallourn and one at Loy Yang, had already failed in the lead up to the extreme heat, but a second unit at Loy Yang is expected to fail on Friday, Ms Zibelman said.
Power is being imported from South Australia to help Victoria cope.
Earlier on Friday, Victorian Energy Minister Lily D'Ambrosio had been assured by AEMO that there was enough power as temperatures reached beyond 40C across the state.
Before the load shedding call, more than 6000 properties experienced power outages overnight due to distribution issues.
Friday's critical demand period will last until 5pm, before a cool change and the Alcoa aluminium smelter - the state's largest energy user - will go offline until the change sweeps the state.
About 10 other companies are also going offline to help the network.
Overnight minimum temperatures of 29.3C at Rutherglen was the northeast centre's hottest night ever since records began 100 years ago, Bureau of Meteorology senior forecaster Michael Efron said.
Suburban Essendon also recorded its warmest night in 17 years, at 30C.
On Friday, parts of northern and eastern Victoria will sizzle in the mid-40s, potentially breaking more records.
Swan Hill, Mildura and Echuca are forecast to soar to 46C or 47C while temperatures across Gippsland, Sale and Bairnsdale will likely reach 45C.
Melbourne is set for 44C, which if reached will be the hottest day in 10 years, since Black Saturday, February 7, 2009 when it reached 46.4C.
Melbourne's cool change is expected about 3pm, moving to the outer suburbs by 4pm, bringing a temperature drop of about 20 degrees within an hour.
But the change brings risk of rain, thunderstorms and dusty erratic winds and there is also a risk of dry lightning, which could spark more fires.
A total fire ban is in force statewide on Friday and a blaze has broken out in East Gippsland, with an emergency warning issued for Timbarra about 11am.
Australian Associated Press