Temperatures across the country have been so high animals are literally falling from the sky due to heat exhaustion.

Harrowing photos taken by a Victorian resident late last week show cockatoos lying dead on the ground.

"The thermometer under the back veranda got to 48.9C today, not an official reading obviously, but it was enough to kill these sulphur-crested cockatoos," he wrote alongside the pictures.

A heatwave struck the state last week, peaking just shy of 48C.

Records have tumbled and bushfires have raged as a result of the heat.

The Jirrahlinga Koala and Wildlife Sanctuary, in regional Victoria, said it had dozens of calls in only hours for hurt animals.

Possums, flying foxes, koalas and other wildlife were "falling out of the sky" as heat exhaustion forced them to plummet from branches.

The sanctuary said its important to remember possums are nocturnal, meaning they're going to struggle to adapt to higher temperatures since they're used to being out at night.

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Victoria sweltered through its hottest December day on record on Friday, with two towns falling just short of 48C.

Horsham, in the state's west, and Hopetoun, in the northwest, recorded 47.9C, exceeding the previous December record of 46.6C at Robinvale on New Year's Eve 1976. It was also Horsham's hottest day ever.

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Cape Otway, on the Great Ocean Road, also recorded its hottest ever day at 43.4C, smashing a record set more than 150 years ago.

Melbourne's temperature fell short of the forecast 44C, reaching a maximum of 43.4C - the capital's hottest day since 1876.

- with AAP