NSW and Victoria continue to burn as air quality in Canberra declared the world's worst_1

As tens of thousands of people rush to evacuate NSW's South Coast, firefighters have been busy tackling more than 110 blazes ravaging the state. 

The bushfire crisis gripping parts of Australia has spiralled into a "national emergency", Labor leader Anthony Albanese told the ABC after Victoria's premier confirmed at least 17 people were unaccounted for.

More than 2000 firefighters are working across NSW where more than 50 fires are burning out-of-control, and just three have been downgraded to a watch and act level.

These were the 229,000-hectare Currowan fire on the south coast, the 130,000-hectare Dunns Road fire in the Snowy Valleys and the 104,000-hectare Green Valley fire east of Albury.

The NSW Rural Fire Service said seven regions are under "very high" fire danger, including the central ranges, the ACT, New England and southern slopes. No total fire bans were declared on Thursday.

But conditions had been worse in the NSW coastal town of Bateman's Bay, which has been besieged by fires in recent days, rating nearly twice as bad as Canberra earlier on Wednesday.

Air quality in Canberra is more than 10 times hazardous levels according to local health authorities, having peaked at more than 20 times hazardous levels on Wednesday.

The smoke is expected to linger over the capital in the coming days, with the Bureau of Meteorology saying high temperatures were trapping the smog there.

Locals in Hobart have been warned about going home after bushfire left a trail of destruction.

Fallen trees and powerlines are among the items posing a hazard on roads towards Pelham, the Tasmania Fire Service warned on Thursday.

The area was previously subject to an evacuation alert and remains at ‘advice’ level as the uncontrolled blaze continues to burn.

“Pelham and surrounding areas … may still be threatened with ember attack and residents are asked to be mindful of changing wind conditions,” the TFS said in a statement, noting that non-residents will not be granted access to the township.

-with AAP/agencies