More than 1,000 people were forced to evacuate their homes in southeastern Australia yesterday as the worst floodwaters to hit the area in a decade threatened to swamp a remote farming town, officials said.

Residents of Coonamble, in central New South Wales, were ordered to leave their homes as the local river threatened to burst its banks, after days of punishing rain unleashed by ex-tropical cyclone Laurence.

"We are looking at a flood peak in the early hours of Monday morning at around 5.5 metres," said Phil Campbell, from the State Emergency Service (SES).

"That particular flood height does give us some concern regarding the levee that does protect 224 properties within Coonamble and, as such, an evacuation order has been issued," he told state radio.

Several towns have already been cut off by the deluge, which has been soaking the drought-ravaged state since Christmas, the SES said.

The weather bureau warned farmers to prepare for week-long isolation ahead of the Christmas floods, and a bureau spokesman said the rain had been the heaviest in the area in a decade.

"As I guess most people are aware, it's been fairly dry for some time... 5.5 metres would probably be the biggest peak (for Coonamble) in the last 10 years," he said.

"Probably the last peak of this sort of magnitude was in 2000."

Waters at nearby Gilgandra and Mendooran were receding after major flooding earlier in the weekend, it added.