SYDNEY (AFP) - Australia's Prime Minister on Thursday (Nov 21) denied his climate policies had caused unprecedented bush fires ravaging the country and insisted his government was doing enough to tackle global warming.

As blazes that have scorched swathes of countryside continued to spread and the country's largest city Sydney was cloaked in hazardous smoke, conservative leader Scott Morrison defended his climate record, saying Australia was "doing our bit".

His comments came after weeks spent refusing to speak about the link between climate change and deadly fires described by the emergency services as unprecedented in number and scale for the early bush-fire season.

"The suggestion that any way shape or form that Australia - accounting for 1.3 per cent of the world's emissions... are impacting directly on specific fire events, whether it is here or anywhere else in the world, that doesn't bear up to credible scientific evidence," he told ABC radio.

As more people in the south-east of the country were told to evacuate their homes, and schoolchildren in Sydney were again forced to play indoors, Mr Morrison dismissed mounting calls for action.

Australia, he said, was "doing our bit as part of the response to climate change", and sought to frame the issue as a global concern.

Scientists, former fire chiefs and residents touched by bush fires have all drawn the link between this season's more intense fires and climate change.

Drought, unseasonably hot, dry and windy conditions have fuelled the unprecedented blazes. Scientists believe many of those factors are made worse by rising global temperatures.