Strong winds and flash flooding from storms overnight also caused widespread damage in neighbouring Queensland state.

A search for a man and woman missing after their car was swept from a flooded causeway in Coomera on the Gold Coast tourist hub was suspended late on Thursday.

Lifeguards on jetskis had earlier joined police in searching for the couple, feared drowned.

Several other people were rescued from stranded cars and some homes were damaged but there were no injuries, officials said.

State Emergency Services spokesman Phil Campbell said at least another 325 people had been evacuated in small towns north of Lismore on the Tweed river near the border with Queensland.

Just two weeks ago farmers were dancing in the rain after downpours delivered the first heavy showers in more than four years to large areas of drought-ravaged eastern Australia. Australia is the world's second-largest wheat exporter after the United States and a major supplier to Asia and the Middle East.

"Drought is not broken by one rainfall event but this is a wonderful start," National Farmers Federation President Peter Corish told reporters.

Rain which began earlier in June allowed farmers to plant winter crops after many had endured three months with barely a drop of rain.

Inland areas of New South Wales that had been dustbowls sprang to life as green seedlings began to appear but the heavy rain was now preventing some farmers from tending to their newly planted crops.

Further south, heavy rain began to fall near Goulbourn, one of the areas worst hit by the drought and which had been close to running out of drinking water.

"It's certainly been helpful but it hasn't been drought-breaking rain by any means," Goulbourn water official Matt O'Rourke told Nine Network television.

Lismore Mayor Merv King said the evacuations were ordered as a precaution even though 10-metre high banks were built in the area after floods in 2001.

Officials said about 500 mm of rain had fallen in the past 48 hours around Lismore and there were fears the floodwaters could overflow the banks.

"Better to be prepared than sorry," King said, adding that roads had been cut around the town and that an evacuation centre had been set up at a local university.

"People should be very careful if they are using the roads and if they haven't got a good reason for going out, stay at home," King said.

About 46,000 people live in and around Lismore, where the main agricultural products are macadamia nuts, cattle and fruit and vegetables.

Flood warnings were issued for towns north and south of Lismore, while emergency services worked to clear up after storms lashed Queensland's popular Gold Coast, triggering small landslides and flooding dozens of homes and businesses.