It comes as emergency services are also brace for "uncontrollable, unpredictable and fast-moving" fires.

Moorabbin had already hit 41.4 degrees while Geelong reached 42.9 just after 1pm.

Stifling conditions are expected across the state with Mildura and Swan Hill forecast to reach 46, while the Mallee region in northwest Victoria could soar to a blistering 47.

The mercury was sitting just below 45 degrees in Mildura at 1.30pm while the temperature hovered at 43.9 in Swan Hill.

By 12.30pm,  a small bushfire was burning near Mount Ellery in Gippsland with residents warned to monitor conditions. Fire crews are at the scene and the blaze is not yet under control.

A scrub and grassfire also broke out at Rosedale, near Traralgon with firefighters called to the blaze at 12.45pm. Twelve tankers and a water-bombing aircraft are currently at the scene.

Authorities say there is currently no threat to residents but urged people to monitor the conditions.

The gusty winds are also expected to stir up dust, prompting a health warning from the state's Environment Protection Authority.

EPA air quality scientist Gavin Fisher said in areas in such as Brooklyn and South Geelong, the air quality would be poor and could increase the risk of health problems for those with heart and respiratory conditions.

Emergency services are on alert with a statewide total fire ban in place after the Bureau of Meteorology predicted temperatures to reach scorching highs on Friday.

Melbourne is forecast to reach 42 degrees — its hottest day in three years— while Echuca, Swan Hill, Kerang and Mildura in Victoria’s north and north-west are forecast to hit 46 degrees.

But the hottest time of the day will hit Melbourne shortly before 4pm when the temperature is expected to soar to 42 degrees.

"We'll see the maximum temperature arrive just before the cool change hits," senior forecaster Tom Delamotte said. "We expect that change to move through the city sometime around 4pm so we'll be seeing the hottest conditions around mid to late afternoon."

Parts of the city's south-west, including Laverton, are predicted to reach a scorching 44 degrees.

Avalon is expected to hit 44 degrees while Geelong has a maximum temperature of 43 forecast.

Life Saving Victoria is urging Victorians to keep safe in the water with many people expected to head to beaches, rivers and pools to cool off.

Preliminary figures compiled by Royal Life Saving Australia show that 48 people drowned from December 1 to January 1, compared with 31 last summer.

Victoria has been among the worst-hit states with 12 drowning deaths so far this summer, just behind NSW and Queensland, with 14 in each state respectively.

A cool change is predicted to come in from Victoria’s south-west in the early morning, reaching Melbourne and the north and north-west of the state about 4pm and crossing into the far east late in the evening.

Wind gusts of up to 70 kilometres an hour are expected to lash Melbourne by 11am and steadily increase as the cool change sweeps the city.

The bureau has issued severe weather warnings for damaging winds of up to 100km/h in the afternoon and a risk of thunderstorms and dry lightning which could spark fires but with little rain.

The hot, dry and windy circumstances could make for a deadly day across the state, CFA Chief Officer Steve Warrington warned.

‘‘We've seen this happen and unfortunately it's unfolded in some cases with loss of life and certainly buildings and structures,’’ he said.

‘‘We know any fires will be uncontrollable, unpredictable and absolutely fast-moving.

‘‘This is the first statewide total fire ban we have had this summer.

"Every corner of the state is facing very high to severe conditions.’’

The wind, Mr Warrington said, will have a ‘‘significant impact on our ability to fight fires should one ignite’’.

The heat and wind are a "a recipe for us to go ‘we’ve got to be on our game’,’’ he said.

"The whole of the emergency services sector is prepped and ready to go. We have 50-odd aircraft ready to fly at any moment."

Mr Warrington said campers or anyone preparing to travel on Friday should re-think or cancel their plans and urged people to stay safe and have fire plans ready.

Country Fire Authority deputy chief officer Gary Cook said the ‘‘most extreme forecasts’’ were for the Mallee and Wimmera districts in the state’s north-west which are forecast to hit up to 47 degrees. ‘‘It’s in the ‘nasty day’ category, there’s no questions about that,’’ he said.

Stay indoors

All Victorians are being urged to stay somewhere cool, to not leave children or pets in cars and to check on vulnerable members of their community including people over 65, infants, toddlers and pregnant or breastfeeding women.

Emergency Management Commissioner Andrew Crisp said now was the time to make or review fire plans.

"This is a timely reminder that if you have not done your preparation, your plan in relation to fire, you'd better get on to it," he said.

"We've got an extreme fire risk danger day [on Friday] across the state of Victoria."

Despite the thunderstorm and dry lightning warning, Acting chief health officer Brett Sutton said there was no risk of a thunderstorm asthma event, as the at-risk period of November and December had passed.

Commuters are being warned to brace for changes to services to keep the public transport network moving during the hottest parts of the day, with heat expected to expand rail and tram tracks.

Public Transport Victoria chief executive Jeroen Weimar said there would be a reduction in services, reduced speeds and bottles of water handed out at stations such as Flinders Street.

Mr Sutton said hospitals and Ambulance Victoria staff were primed for extra heat-related admissions.

Holiday-makers camping in state parks and near beaches are being urged to take safety precautions.

‘‘Visitor safety is also a personal responsibility,’’ Parks Victoria chief operating officer Simon Talbot said.

‘‘With the current hot weather, we urge visitors to plan ahead, review weather conditions and carry appropriate equipment."

By about 7pm on Friday the temperature is forecast to have dropped to about 22 degrees before an overnight low of 17.

Cooler conditions will continue for the weekend with a top of 21 predicted for Saturday and a sunny 23 forecast for Sunday.

The risk of fire has also shut a number of parks across the state including:

• Ferntree Gully picnic ground (including the 1000 Steps)
• One Tree Hill Picnic Ground
• Doongalla Picnic Ground
• Valley Picnic Ground
• Eagles Nest Picnic Ground
• Silvan Reservoir Park
• Grants Picnic ground
• Olinda Falls
• Kalorama Park
• Sherbrooke picnic ground
• O’Donohues picnic ground
• Dandenong Ranges Botanic Gardens (formerly National Rhododendron Gardens)
• William Ricketts Sanctuary
• Alfred Nicholas Memorial Garden
• George Tindale Memorial Garden
• Pirianda Garden
• Jumping Creek Reserve
• Norman Reserve
• Koornong Reserve