Torrential rain that began Monday proved unrelenting, with more than 250 millimeters (9.8 inches) falling in the area in 24 hours, forcing many shops in the Byron Bay town center to close as roads were cut off by rising water levels.

Byron's normally buzzing high street -- lined with popular restaurants, bars and clothing stores -- was all but empty Wednesday morning, transformed into a river by the mud-brown floodwaters.

In the nearby town of Alstonville, 420 millimetres of rain fell in 24 hours.

By Wednesday morning, there were 10 evacuation orders in place across the affected region, urging thousands of people to leave their homes for higher ground.

For weeks Australia's east has been smashed by extreme weather, fuelled by La Nina weather patterns and climate change.

Record rainfalls and deadly flooding have killed at least 22 people since early February.

In Lismore, which last month was devastated by a record 14.3-metre (47-foot) floods, the town's levee was breached on Wednesday morning, emergency services confirmed.

The town's local member of parliament Justine Elliot warned residents on social media that the levee's siren would not sound because of a malfunction.

"You MUST get out now," she wrote on Twitter Wednesday.

When the Lismore levee was breached just weeks ago, floodwaters rushed into the town's centre, rising to the second storey of many homes and businesses, stranding hundreds of locals on their roofs.

Many Lismore residents were rescued by their neighbours, who braved the floodwaters in private boats and even kayaks because emergency services were completely overwhelmed by calls for help.

It is predicted that the floodwaters in the town could this week reach a height of 11.4 metres, which would be a major setback to the ongoing clean-up effort.

"Unfortunately overnight our worst fears have been realised," emergency services minister Stephanie Cooke said Wednesday.

Heavy rain across already saturated land had caused "flash flooding in a number of communities", she said, and there were also a number of landslides across the region.

During a visit to Lismore in the aftermath of last month's floods, Australia's prime minister Scott Morrison said the country was "getting hard to live in because of these disasters".

"We are dealing with a different climate to the one we were dealing with before. I think that's just an obvious fact," he said at the time.

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© Agence France-Presse