An out-of-control fire was last night raging towards residents in Victoria's northeast who have been warned it's too late to leave their homes.

The Country Fire Authority (CFA) issued an emergency warning for Barnawartha, Indigo Upper and Indigo Valley.

"You are in danger, act now to protect yourself. It is too late to leave," the CFA said.

A predicted southwesterly change hit the area with wind gusts up to 80km/h as conditions rapidly deteriorated.

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All of the state's firefighting aircraft had been dispatched to help crews on the ground.

Emergency Management Commissioner Craig Lapsley said they were battling numerous fires across Victoria.

He said the 4000ha Scotsburn fire, near Ballarat, was of critical concern and at least eight buildings had already been destroyed.

The volatile conditions at Scotsburn had caught many off guard, he said.

Three CFA crews, in two separate incidents, were lucky to escape when their vehicles became trapped when a storm cell ran into the smoke plume at Scotsburn, pushing the fire to the west while the winds hit from the north.

The trapped crews activated the sprinklers over the trucks and huddled under fire retardant blankets until the danger had passed.

It's believed the Scotsburn fire was started by a spark from machinery operating in a paddock.

Crews were also battling fires, all started by lightning, near Lorne in the Otway National Park, near Buxton and in East Gippsland.

They were also keeping an eye on a contained but out of control grassfire at the foothills of the Dandenong Ranges.

Premier Daniel Andrews applauded firefighting efforts, saying the weekend's operation was another example of fire crews putting their lives on the line to protect Victorians.

Watch and Act warnings were in place for Wandin North, Scotsburn, Barnawartha and Grenville. Advice messages were issued for Lorne, East Gippsland, Shepparton North and Buxton.

The CFA has also issued a Watch and Act alert for nearby areas.

"The fire could impact Indigo Valley, Wooragee, Indigo Upper, Leneva West or Yackandandah any time," the CFA says.

Those residents were told to leave.

Last night a large bushfire raging through thick scrub north of Newcastle had broken containment lines as crews battle dozens of blazes across New South Wales in hot, dry conditions.

The fire has burnt 350ha of scrub near the Williamtown Airport, and is now blowing south towards Nelson Bay Road. People living along Nelson Bay Rd between Richardson Rd and Medowie Rd have been warned to be vigilant against embers, after the blaze "spotted" across its southern lines.

Smoke forced the closure of Nelson Bay Rd and Medowie Rd, with firefighters working to contain the blaze as a "watch and act" alert was issued. Crews have responded to 43 grass and bush fires across the state as hot, dry and windy conditions from South Australia and Victoria push into NSW. Total fire bans have been issued for eight areas across southern and western NSW as well as the ACT, with severe fire danger ratings in place across the same regions.

After a week of extreme conditions, a cool change has finally arrived in South Australia. Crews were on high alert on Saturday after four days of temperatures above 40C, but there were cooler conditions yesterday.AAP