Three hundred animals have been evacuated from a wildlife park north of Sydney as massive bushfires encircled Australia's largest city and foreign firefighters arrived to relieve beleaguered local forces.

Walkabout Wildlife Park said it had shipped out lizards, dingoes, peacocks and marsupials, as firefighters battled more than 100 fires up and down the eastern seaboard.

"This fire has been doing some crazy things, so we have to be prepared," general manager Tassin Barnard told AFP.

Prolonged drought has left much of eastern Australia tinder dry and spot fires have raged every day for the past three months, leaving firefighters struggling to cope.

New South Wales rural fire chief Shane Fitzsimmons said some US and Canadian firefighters had arrived to help out, easing the strain on the exhausted largely volunteer Australian force.

The incident-management and aviation specialists will help ease "fatigue and crew rotations" he said.

"We are not only appreciative of their presence here today, but of their sacrifice," said Mr Fitzsimmons, who has become a fixture on Australian television screens for weeks, updating the public on blazes in towns, national parks and backwaters.

"They are volunteering to sacrifice time from loved ones, from families, to give up that special time of the year around Christmas and New Year to come down here and lend us a hand," he said.

More than 600 homes have been destroyed and six people have died since the crisis began in September.

That is many fewer than Australia's deadliest recent fire season in 2009 when almost 200 people died, but 2019's toll belies the scale of devastation.

Millions of hectares have burned - the size of some small countries - across a region spanning hundreds of kilometres.

Bushfires are common in Australia but scientists say this year's season has come earlier and with more intensity due to a prolonged drought and climatic conditions fuelled by global warming.

The fires have taken a toll in Sydney and other major cities, which have been blanketed in toxic smoke for weeks and occasionally sprinkled with snow-like embers.

Mr Fitzsimmons said he could not "overstate the effect that this profound drought is having" as he warned of a long, painful summer ahead.

"There is an absolute lack of moisture in the soil, a lack of moisture in the vegetation ... you are seeing fires started very easily and they are spreading extremely quickly, and they are burning ridiculously intensely."