Australian authorities retrieved the bodies of a mother and her two children from post-cyclone floodwaters in the state of New South Wales. Picture: Tracey Nearmy/Reuters

Sydney – Australian authorities retrieved the bodies of a mother and her two children from post-cyclone floodwaters in the state of New South Wales on Tuesday.

The family's car was swept into the surging Tweed River in the town of Tumbulgum on Monday, drowning the 43-year-old woman, her seven-year-old son and 11-year-old daughter.

Another daughter, eight-years-old, escaped from the car with just minor cuts.

"She's obviously traumatised by the incident," Tweed Byron's police inspector Mick Dempsey told reporters.

Four police divers from Sydney recovered the bodies on Tuesday afternoon.

The conditions in the area are "horrific" with many of the roads "treacherous," an emergency services official said.

Tumbulgum has a population of just 400 and is still under evacuation orders due to surging floods.

The death toll from flood-related events following Cyclone Debbie, which hit the state of Queensland last week, has now risen to six.

A huge clean-up operation is continuing across northern New South Wales and southern Queensland as many coastal towns have been left devastated by the cyclone, torrential rains and floods.