Australia is cooling down after another day of deadly heat with temperatures in three states soaring into the 40s, including record highs in Melbourne.

Vast tracts of South Australia are preparing for another baking day of catastrophic fire risk after yesterday's 40C-plus temperatures.

A student at a top private school has been charged with arson after a fire that damaged two classrooms.

Suspicion that arsonists may have been behind a series of spot fires near Rockhampton in central Queensland, lit while firefighters were battling a "terrifying" wildfire, has fuelled community anger.

A fire that gutted the Christchurch "House of Horrors" is a "turning point" for the community, Mayor Bob Parker says.