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Victoria Premier Jacinta Allan says the discovery of a body in the wake of a bushfire on the weekend is " incredibly devastating", as firefighters continue to battle blazes through the state.

Allan told Today there were 12 active bushfires in Victoria this morning, but as of 8am AEDT, emergency warnings were in place only for two of them.

Fire crews across Victoria are battling multiple blazes burning at an emergency level as extreme winds and high temperatures create "catastrophic" conditions.

Two major fires at Longwood and Walwa continue to burn out of control with multiple properties confirmed destroyed.

Three people - two adults and a child - also remain unaccounted for.

Across the border, NSW is in the grips of an extreme heatwave with health authorities warning people to avoid the health risks that come with it.

A major bushfire that has des troyed homes and left three people missing in central Victoria has created scenes that a local firefighter has likened to an "atomic bomb".

The out-of-control blaze in Longwood has already burnt more than 48,000 hectares of land around the townships of Ruffy, Tarcombe, Caveat and Dropmore as the state battles the most dangerous conditions since the Black Summer fires.

In the small town of Ruffy, south of the fire, at least 10 homes have been destroyed.

Three people, including two children, are dead after a truck and a car collided in regional Victoria this morning.

Emergency services were called to the crash scene at the intersection of Eurambeen-Streatham Road and Mount William Road at Stoneleigh, west of Ballarat, shortly after 9.30am.

Police said the car appeared to have rolled and been crushed.

An adult and two children died at the scene.

An adult who was trapped in the car suffered life-threatening injuries and is expected to be airlifted to hospital.