Tens of thousands of Australians have been forced to evacuate as torrential rains caused the worst flooding in a decade on the country’s southeast coast region.

The rains submerged town centres, washed away homes and cut power lines.

At least 13 people have been killed since the extreme weather arrived late last week, the latest four deaths recorded in the worst-hit town of Lismore in New South Wales.

“This is terrible. This is terrible. One life lost is too many,” said New South Wales Deputy Premier Paul Toole.

Emergency crews carried out 300 flood rescues after getting 2,200 requests for help overnight. Military helicopters airlifted stranded people from rooftops, while stranded motorists and animals were rescued from a bridge after fast rising waters submerged both ends.

A deadly storm front barrelled south on Wednesday towards Sydney, home to more than 5 million people.

The Bureau of Meteorology said Sydneysiders should brace to receive months worth of rain in a few hours, as officials reported that Warragamba Dam, the city’s main source of water, began overflowing on Wednesday morning.

“Today, the focus is on Sydney. We are expecting heavy rainfall over the afternoon into the night and into tomorrow,” Toole warned in a news conference.

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