As many as 10,000 koalas — a third of New South Wales' total population — are estimated to have perished this summer from bushfires and drought, an inquiry has heard.

Key points: A wildlife expert says a third of all koalas in NSW may be dead from bushfires and drought

A wildlife expert says a third of all koalas in NSW may be dead from bushfires and drought He has called for a statewide census of koalas to better understand the impact

He has called for a statewide census of koalas to better understand the impact A tendency to climb upwards when scared disadvantaged the koala this bushfire season

Rappville and Wardell in northern NSW were among the worst-affected areas, with up to 80 per cent of the local koala population killed by bushfires, according to a World Wide Fund for Nature (WWF) study.

WWF conservation scientist, Dr Stuart Blanch, argued the marsupial should be listed as endangered following the estimated loss of a third of the total NSW koala population.

"What I've heard from people doing the surveys is that we might have lost 10,000 koalas from the fires and the droughts," he told the committee.

"It's brought forward a 2050 extinction projected timeline for most of the populations across the state by years."

He also called for another statewide census to count koalas, calling the estimate of 36,000 koalas in NSW "outdated".

Spirit recovers in Currumbin Wildlife Hospital after being rescued from NSW bushfires. ( Facebook: Currumbin Wildlife Hospital )

The state parliament inquiry, which has been running since last year, has been delving into the current state of koala populations and habitat in NSW.

The committee also heard from Dr Kellie Leigh, who said at least 1,000 koalas have been impacted by bushfires in the greater Blue Mountains area over the summer.

Dr Leigh, from the Science for Wildlife charity, rescued a dozen koalas from the Gospers Mountain blaze and helped relocate them to Taronga Zoo.

A koala rescued from a blaze in Crowdy Bay National Park by Taree-based Koalas In Care inc volunteers. ( Supplied: Koalas In Care Inc )

"Four different koala populations that we know of, which have hundreds in each population, have been impacted. Some have had 100 per cent of their habitat burnt out," said Dr Leigh.

"[But] we just don't know what the full impact is yet, because we have to wait until it's safe to go in, to see what's survived."

The state's unprecedented bushfire season saw more than 5 million hectares of land razed by fires, with at least two 'mega-fires' each scorching more than 500,000 hectares.

An injured koala is rescued in the midst of a bushfire. ( 9News )

More than a billion animals were killed by fires in NSW this bushfire season, while hundreds of billions of invertebrate are thought to have perished.

As much as 30 per cent of koala habitat was destroyed state-wide, putting the endangered species further at risk of extinction.

A naturally dense pelt and a tendency to climb upwards when threatened has disadvantaged the koala population, as bushfires were recorded travelling as fast as 60 kilometres an hour.

A koala being treated at the Koala Hospital in Port Macquarie. ( ABC News: Kirstie Wellauer )

Recent widespread rainfall led to the containment of every single fire still burning in the state last Thursday, according to the NSW Rural Fire Service.

Committee Chair Cate Faehrmann tod the ABC her committee has heard "overwhelming evidence of the need to protect more koala habitat as a result of the devastating loss caused by these fires".

The committee is due to report back findings mid-2020.