SYDNEY - AUSTRALIAN firefighters battled dozens of bush blazes on Friday as record-breaking hot weather sparked 'catastrophic' warnings in two states, just months after the country's worst ever wildfire disaster.

Major lightning storms set off about 100 blazes in South Australia alone, most of which had since burned out, according to the state's Country Fire Service. Emergency crews also battled scores of fires in the most populous state of New South Wales, some on the outskirts of Sydney, the Rural Fire Service (RFS) said.

More than a quarter of the state was considered at catastrophic risk and lightning strikes set two homes in the city ablaze.

Hundred-year records tumbled this week as the south and south-east of Australia sweltered through a heatwave which dried out vast tracts of bush and farmland already in the grip of a decade-long drought.

Flights were delayed due to the unseasonable heat, thunderstorms, strong winds and the effects of smoke on visibility, air traffic officials said. The first 'catastrophic' or 'Code Red' warnings - a new category introduced after February's deadly Black Saturday fires - were declared in parts of the two states, under which residents are strongly advised to flee their homes.

Code Red conditions are considered on a par with those experienced ahead of Black Saturday, Australia's worst disaster of modern times which killed 173 in the state of Victoria and razed more than 2,000 homes.