A thirsty koala hit by South Australia's extreme heat has stopped a group of cyclists in their tracks, drinking water from them and clambering onto a bike as temperatures soared on Friday.

Key points: The koala was on the road, prompting the cyclists to stop and help

The koala was on the road, prompting the cyclists to stop and help It climbed a bike to get a drink on a day that hit 42C in Adelaide

It climbed a bike to get a drink on a day that hit 42C in Adelaide Fires have destroyed 86 homes in the Adelaide Hills

Cyclist Anna Heusler was with a group of friends riding down Norton Summit Road in the Adelaide Hills when they saw the koala sitting in the middle of the road.

"This koala walked right up to me as I was descending and climbed up onto my bike while I gave him water," she wrote on Instagram.

"There were about a dozen cyclists around me watching this (all men) and several commented that it was genuinely the best thing they've witnessed. What a truly wonderful experience."

This thirsty koala climbed up onto a bike as cyclists gave it water during a 40C day in Adelaide. ( Instagram: Bikebug2019 via Storyful )

The temperature around Adelaide hit 42 degrees Celsius on Friday afternoon.

Ms Heusler said it was the "best thing ever" to happen to her on a bike ride and praised firefighters for their work in the region.

The current bushfires across large parts of Australia have taken a heavy toll on the koala population.

On Friday, federal Environment Minister Sussan Ley told AM that an estimated 30 per cent of koalas on the New South Wales mid-north coast had died in the fires so far.

Wildlife carers around the country have been inundated with koalas and other native animals injured in the fires.