A 15-month-old baby was rescued from a locked car and taken to hospital on a day when temperatures in Victoria hit more than 40C for much of the state.
The infant was one of four children who had to be rescued from vehicles on Friday but was the only one taken to hospital, Ambulance Victoria's health commander Paul Holman said.
"The child taken to hospital was 15 months old, only in that car for a very short time and in that very short time, became visibly distressed and needed medical transport," Mr Holman told reporters.
He said 11 children were also rescued on Thursday but none had to be taken to hospital.
"It really shows you such a short time how vulnerable these little ones are," the commander said.
It was the hottest day in Melbourne for the past two years with the mercury hitting 42C but a cool change dropped temperatures between by up 12 degrees at 3pm.
However, there was little relief for people in parts of regional Victoria, with temperatures hitting 45.8C in Walpeup and 46C in Hopetoun, both in the northwest.
Despite the staggering heat only 10 bushfires had been reported across the state, with the most significant at Mt Misery in the state's southeast being contained within 90 minutes.
Emergency Management Commissioner Craig Lapsley said Victorians had heeded total fire bans across the state but warned the situation could change.
"It's a hot day and we are obviously quite pleased to see that there has only been around 10 fires reported today, those are bushfires," he said.
"We started the day with no fires, all the fires that were burning yesterday were brought under containment and control so that was a good start for Friday."
However, the fire risk remains high and will continue for much of the weekend for the northern parts of the state, Mr Lapsley said.
V/Line has warned speed restrictions will apply again on Friday, and the regional lines also have coach replacements due to planned maintenance.
Metro Trains has also warned passengers to expect delays of up to 15 minutes because of the extreme heat.
And at the Australian Open tennis, players battled on without organisers halting play on outer courts or closing the roofs on the main stadiums as they can when certain heat thresholds are met.
Frenchwoman Alize Cornet suffered heat stress and needed medical attention in her third-round encounter with Belgium's Elise Mertens on Friday.
The incident followed French star Gael Monfils becoming distressed during his second-round loss to six-time champion Novak Djokovic on Thursday.
