A koala, whose dramatic rescue in NSW's Port Macquarie was captured on video Tuesday, has been given a "50-50" chance at recovering from its injuries, 9News reported.

A spokesperson from the Port Macquarie Koala Hospital said the marsupial's "feet are completely burnt and he has burns to his chest and stomach."

"He has been bandaged and given antibiotics but will take a lot of looking after, if he pulls through," the spokesperson told 9News.

More than 350 koalas were feared to have been killed by bushfires in New South Wales, according to animal experts.

In Sydney, more than 50 people were treated for asthma and breathing-related problems on Tuesday as smoke blown from NSW bushfires engulfed Australia's largest city in thick smoke.

Air quality dropped to "hazardous" levels in the Sydney area overnight Tuesday, according to the New South Wales Bureau of Meteorology.

"I was up checking all our windows and doors were shut because it smelt like our house was on fire. A lot of my colleagues are complaining that it burns their eyes being in it and a lot of issues with asthma in our office," Adele Bryant, who lives close to Rouse Hill in Sydney, told CNN.

Another hot and dangerous day is forecast for Thursday, with windy conditions moving further east.

The drought and the fires are the most urgent symptoms of Australia's climate crisis. Disasters like the fires and floods have devastated the livelihoods of farmers and wrought millions of dollars' worth of damage. The country is getting hotter and drier, and the rains have stopped coming.