The Lancefield blaze was one of 100 burning across Victoria, as high temperatures and strong winds fuelled the bushfire risk throughout the day.

The Country Fire Authority upgraded a watch-and-act message to an emergency warning for the Cobaw, Lancefield, Benloch and Nulla Vale areas in the Macedon Ranges shortly after 2pm.

Firefighters have been unable to stop the fire, which has crossed Three Chain Road and is moving quickly towards Lancefield.

A wind change around 4pm, caused the fire to head in a north-easterly direction towards Benloch and Nulla Vale.

Spot fires and ember attacks are starting up to 2.5 kilometres ahead of the main fire.

Smoke billowing from the blaze in the Macedon Ranges is visible from Melbourne's northern suburbs, and is showing up on the Bureau of Meteorology rain radar.

Lancefield Hotel manager Tammy Notman said shops in the town had shut and the local primary school had been evacuated.

"It's really eerie," she said. "You can't see the sun. The sky is full of smoke."

Premier Daniel Andrews said 190 properties were at risk and issued a stern warning to Victorians.

"The fire season is here right now," Mr Andrews said.

"It is absolutely on us.

"It is going to be a long, hot, dangerous summer."

Watch and act

A fire has broken out at Calder Park, closing the Calder Freeway in both directions about 4.30pm.

The CFA issued a watch and act warning about 4pm for Calder Park, Sydenham, Hillside (Melton), Sydenham Park, Keilor North and Taylors Lakes.

There is a medium 30 hectare grassfire travelling fast in a northerly direction from Calder Park Drive towards Victoria Road and Darlington Grove

Due to a fire located near the Calder Park Thunderdome, all westbound lanes have been closed on the Calder Freeway at Kings Road.

Westbound traffic will be detoured via Kings Road on to the Melton Highway.

At this stage, eastbound traffic can still use the Calder Freeway.

Smoke is visible in the surrounding areas.

Earlier, a watch and act message was issued for Nar Nar Goon North, Maryknoll and Tynong North shortly before 3pm.

A small grassfire was travelling quickly in an easterly direction from Pooley Road toward Mortimer Road, about 70 kilometres south-east of Melbourne.

A watch and act alert was also issued in the Macclesfield area, 50 kilometres east of Melbourne.

A small controlled bushfire is near Yellingbo-Macclesfield Road and Ewen Road, but authorities are concerned a forecast wind change could push the fire in a north easterly direction towards Nangana.

A watch and act has also been issued for Strath Creek in Central Victoria. The CFA says the wind change is expected anytime between 4.00pm and 6.00pm, which will cause the fire to change directions towards Trawool and Kerrisdale.

Total fire ban

Hot and gusty conditions have led to Victoria's earliest ever total fire ban.

Bans were declared in six of Victoria's nine fire districts on Tuesday after a run of hot days and a sweltering night baked already tinder-dry areas across the state.

Smoke from Lancefield fire reported in large areas including areas of outer Melbourne - showing on BoM rain radar pic.twitter.com/pTpsFqo3va— CFA Updates (@CFA_Updates) October 6, 2015

The last time a total fire ban was declared this early in the bushfire season was on October 16 in 2005.

Country Fire Authority state control centre spokesman Gerard Scholten said the ban had been enacted even in areas of low to moderate fire-danger.

Mr Scholten said the ban stopped people burning off and forced them to extinguish any existing fires ahead of a forecast 35-degree day in Melbourne, and severe winds throughout the state.

Firefighters on alert

Firefighters are on high alert as a cool change crosses Victoria, bringing strong gusty winds that can turn a long, thin flank of a fire into a threatening front in an instant.

Mr Scholten said crews were working hard to extinguish any small fires.

"The change is going to bring strong, gusty winds and that's a recipe for disaster if there's any fires going," he said.

The predicted cool change has passed through Warrnambool and is due to reach Melbourne between 3.30pm and 4pm.

"Our major priority is to jump on any fires that start between now and then," Mr Scholten said.

Watch and Act warning

More updates are available from the Vic Emergency website.

A grassfire that threatened a steel factory on the Mornington Peninsula earlier on Tuesday is now believed to have been started by a burn-off.

CFA deputy incident controller Arthur Haynes told Fairfax radio station 3AW that 26 crews were sent to the fire on Denham Road in Tyabb just before 7am.

The fire was brought under control just before 9am but had threatened a nearby BlueScope steel factory.

The Bureau of Meteorology has issued a severe weather warning for damaging winds for most of the state.

A 121km/h gust was recorded at Mount Buller early on Tuesday, while winds up to 100km/h are expected in the south of the state throughout the day.

Tuesday has been declared a day of total fire ban in the Mallee, Wimmera, South West, Northern Country, North Central and Central (includes Melbourne and Geelong) districts.