He said that 17 local government areas had been declared disaster zones in an “unprecedented situation”, and urged people in Sydney to evacuate if they are given the order by emergency crews.

Worsening rain was expected to hit Sydney in the early hours of Thursday morning local time. Australia’s Bureau of Meteorology said that Sydneysiders should brace for a month’s worth of rain in a few hours.

Stephanie Cooke, the New South Wales emergency services minister, told ABC: “Hundreds of thousands of people have been impacted by this event. It is not over by any stretch of the imagination.”

The disaster raised questions about how prepared Australia was for being at the forefront of severe climate change, according to one academic expert.

“Despite decades of warnings from scientists about climate change, Australia is unprepared for the supercharged weather that it is now driving,” said Prof Hilary Bambrick, an environmental epidemiologist at the Queensland University of Technology, who led the health impacts assessment for Australia’s national climate change review.

Military helicopters airlifted stranded people from rooftops, while stranded motorists and animals were rescued from a bridge in northern New South Wales after fast-rising waters submerged both ends.