The Australian Energy Market Operator has directed providers to begin load shedding, due to the strain on the network as a result of the heat.
AEMO announced scheduled power supply interruptions to affect 60,000 Victorians would start at midday and last two hours because the sweltering heat had placed a high demand on the state's system.
The planned short-term outages are designed to prevent more widespread blackouts.
An afternoon cool change, expected to bring thunderstorms and prompt a 15C drop in temperature, is expected to take the strain off the system.
Earlier, State Energy Minister Lily D'Ambrosio insisted the state would not have blackouts despite a third coal-fired unit experiencing a fault overnight.
"Blackouts are something that absolutely will not be a feature of today or a possibility," she said.
The more-than-6000 properties that have experienced power outages so far are due to distribution issues and not supply, she said.
Friday's critical demand period will be 12pm to 5pm, before a cool change.
"We have three units down, we have a total of more than 1000MW that are no longer available to Victoria as a result of faulty units and that's becoming more and more the case as they get older and are harder to maintain," Ms D'Ambrosio said.
Demand for power in Victoria is higher than anticipated, at almost at a record high of 9600MW, the highest in many years, she said.
"With these increased temperatures, longer, hotter more extreme summers because of climate change, occurrences like yesterday and today unfortunately will become more frequent and we need to be ready," she said.
Experts expect the units in Latrobe Valley to be down for "a number of days".
At this stage, the market operator is confident there is more than sufficient energy supply in reserve that can be used, Ms D'Ambrosio said.
It was a sleepless night for many with heat records broken across the north east.
Rutherglen went down to 29.3C, their 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 30 degrees.
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.
"I think we will hit the 40C mark late morning or midday in the Melbourne area with that temperature peaking just before the change arrives," Mr Efron said.
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.
However, the state's north east will have to wait until Saturday afternoon for the change.
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.
