(AFP) - The Australian military has begun the seaborne evacuation of hundreds of people trapped in a fire-ringed southeastern town, as the country braced for yet more catastrophic conditions.

A navy landing craft from the HMAS Choules docked in the town of Mallacoota, where residents trapped on the foreshore since New Year's Eve clambered aboard with family, pets and a few belongings.

"Around 1,000 people should have been evacuated out of that area by this afternoon," Prime Minister Scott Morrison said.

At least 20 people have died, dozens are missing, and almost 500 homes have been destroyed, in an unprecedented months-long bushfire crisis that has torched an area roughly double the size of Belgium.

But with temperatures expected to rise above 40 degrees Celsius (104 Fahrenheit) again on Saturday, a state of emergency has been declared across much of Australia's heavily populated southeast.

Thousands of residents and tourists have been heeding warnings to flee a popular 300-kilometre (190-mile) length of coastline, with queues of cars stretching toward Sydney and Canberra.

New South Wales Transport Minister Andrew Constance called it the "largest evacuation of people out of the region ever".

On the road north of Nowra, families sat amid the haze in cars loaded with dogs, surfboards and bicycles, with traffic at a virtual standstill.

Military aircraft have also been working with emergency crews to deliver relief supplies to isolated areas.

Victoria premier Dan Andrews said "satellite phones have now been dropped into a number of regions along with water and emergency supplies".

- Political fallout -

Conservative Prime Minister Scott Morrison -- who was pilloried for holidaying in Hawaii as the country was ablaze -- has come under renewed criticism for his handling of the crisis.

Visiting the hard-hit town of Cobargo, Morrison encountered a tearful young mother and a volunteer firefighter who both refused to shake his hand, before returning to his motorcade amid a volley of abuse.

"You won't be getting any votes down here, buddy," one resident yelled. "This is not fair. We are totally forgotten down here," another said.

Morrison's Liberal ally and local parliamentarian Andrew Constance told 7 News "the locals probably gave him the welcome that he probably deserved".

"The feeling is bloody raw and it's raw for a reason," he added, underscoring that grieving communities now face the prospect of again being without electricity or communications.

"People are frustrated. People have suffered great loss. They're feeling very raw," Morrison said. "I understand how people are feeling and however they wish to respond is a matter for them."

"I don't take it personally."

With no sign of let-up in the fires, Morrison said he was "inclined not to proceed" with a visit to India in nine days' time.

The crisis has also touched cities like Sydney and Melbourne, home to several million people.

The blazes on Friday again shrouded Melbourne and Australia's capital in smoke, forcing the Canberra International tennis tournament to be relocated.

Acrid smoke haze has travelled as far as New Zealand, turning the air over glacier peaks brown.

Authorities in Wellington said New Zealand would be sending a further 22 firefighters to Australia to help.

© Agence France-Presse