New South Wales, Australia’s most-populous state, has declared an emergency as the heatwave that’s produced the hottest day on record exacerbates devastating bushfires.

Today’s catastrophic warning, the highest level of danger, means fires could spread rapidly and will be extremely difficult to control. It is the second such warning for greater Sydney this season.

“We are expecting another very dangerous, another very difficult day today given the widespread geographic area of catastrophic fire danger ratings,” New South Wales Rural Fire Service Commissioner Shane Fitzsimmons told a news conference.

“Catastrophic fire danger is as bad as it gets.”

The crisis could lead to road closures and diversions, potentially disrupting Christmas travel plans for thousands of Sydneysiders pouring out of the city for a summer break along the coast.

Prime Minister Scott Morrison yesterday said he would cut short his vacation in Hawaii and apologised for taking leave while the wildfires ravage Australia, reflecting the political pressure building on his government that denies the blazes are linked to climate change.

In New South Wales alone, eight people have been killed, more than 6 million acres – an area the size of Massachusetts – have been burnt out and 800 houses destroyed since the fire season started unusually early this year. Fires are also raging in South Australia, Victoria and Queensland.

On Wednesday, the average maximum temperature across Australia reached 41.9°C, surpassing the record 40.9°C set a day earlier, according to the weather bureau.

On Thursday it reached 41°C, meaning those three days were the three hottest ever recorded. A temperature of 36°C is forecast for Sydney today.