Police are investigating the potential deliberate ignition of a fire which sparked an emergency evacuation alert in Victoria, where the threat remains amid changing winds.
The grass fire near Little River, 50km southwest of Melbourne, started from three separate points just before midday on Friday and quickly burned southwards.
"Victoria Police are looking into it but it's very, very early days in relation to the investigation," Emergency Management Commissioner Andrew Crisp told reporters when asked of the fire's cause.
The inferno crossed a rail line, halting train services bound for Geelong.
Nearby residents were ordered to evacuate, with a respite centre set up nearby.
As the threat eased, residents of Brophys Crossing, Cocoroc, Point Wilson, Werribee South, Little River, Mambourin, Tarneit and Wyndham Vale remained on high alert pending changing conditions.
The Little River fire was contained but not under control, with firefighters expected to work through the night.
The Country Fire Authority said it was concerned about a forecast wind change forecast for about 10pm, which could exacerbate the fire front facing Werribee.
The Little River inferno was among 19 fires started in the state on Friday mid-morning as temperatures soared to 40C.
Horsham and Hopetoun in the northwest reached 42C and Melbourne hovered between maximums of 37C and 39C.
Avalon and Geelong nudged just over 40C breaking records for those towns for early December.
"It is evident that summer has really hit the state of Victoria," Mr Crisp said.
"We have had the heat, we have had the wind and in total about 19 fires across the state up to this particular point in time."
One firefighter was taken to hospital suffering smoke inhalation but there were no reported injuries.
A wildlife sanctuary west of Melbourne rushed to evacuate up to 30 animals as the Little River fire closed in.
Mt Rothwell Biodiversity Interpretation Centre was not in the direct path of the fire, but staff worked to evacuate dingoes, bandicoots and quolls in case of a wind change.
Staff acted to get the animals off the property, but there was nothing to be done for about 1000 animals that freely roam the 420ha private sanctuary.
Near Ballarat, crews continued to battle high winds as they fought a bushfire that started on Thursday.
The blaze destroyed a shed after it spread south from Nash's Road at Buninyong and scorched more than 40 hectares, sparking an emergency warning.
As of Friday afternoon it remained under control but authorities warned residents from Durham Lead, Grenville and Scotsburn to stay alert.
A total fire ban is in place for the Wimmera, Mallee and Northern Country.