It could take a year for Rockhampton to recover from disastrous floods, the Australian town's mayor said Thursday, as the waters threatened the neighbouring state of New South Wales.

"I think that this could drag on for 12 months," Mayor Brad Carter said, adding that it would take three weeks before Rockhampton's airport reopened, even though the floods appeared to have peaked just below the expected level.

"It looks like it's peaked, it's plateaued and it's showing signs of dropping," he told the Nine Network. "We expect the river system to go down very slowly."

Meteorologists warned Thursday of "heavy rainfall leading to localised flash flooding" elsewhere in Queensland. "This may add to the existing river flood situation," Canberra's Bureau of Meteorology said in a severe weather warning.

The floods, which cover an area as big as France and Germany and have affected some 200,000 people, are expected to spread into the neighbouring state of New South Wales, Australian Associated Press reported Thursday.

The state premier Kristina Keneally and emergency services minister Steve Whan are to visit the inland community of Goodooga, population 300, Thursday to inspect preparations.

It is likely to the first town in New South Wales to be affected by floodwaters and was expected to be isolated for between two and six weeks, AAP said, without citing a source.

Queensland premier Anna Bligh said Wednesday that the flooding was unprecedented in her state and had now directly affected 40 towns, raising the number from 22 announced previously.

She said waters that have flooded dozens of mines and closed railways and ports would send coal and steel prices soaring, adding that the state produces about half of the world's coking coal used to make steel.

Queensland Resources Council has said the floods have already cost one billion dollars (one billion US) in delayed coal production, while the state's resources minister says the industry is losing 100 million dollars a day.

"Seventy-five percent of our mines are currently not operating because of this flood, so that's a massive impact on the international markets and the international manufacture of steel," Bligh told the Seven network TV station.

"Without doubt, this disaster is without precedent in its size and its scale here in Queensland," she added.

Tonnes of sludge pouring into the sea as a result of the floods threaten the iconic corals of the world-famous Great Barrier Reef, scientists have warned.

James Cook University researcher Michelle Devlin said floodwaters carrying debris and pesticides spelt a harmful "cocktail" for the world's biggest reef, a delicate ecological treasure and a major tourist attraction.

"This is a really massive event," Devlin told AFP Wednesday. "It has the potential to shift the food web, it has the potential to shift how the reef operates."

"There is just going to be this cocktail of water containing a lot of things that they (the corals) wouldn't necessarily have seen before," she added. "It is fresh, warm water and that will stress corals out as well."

Devlin said any plume would likely stretch from the reef's southern tip to the scenic Whitsunday Islands, and may in some areas damage sea grass beds -- a feeding ground for dugongs -- or allow damaging crown of thorns starfish to flourish.

Snakes and marauding crocodiles were among the hazards for the besieged residents of steamy Queensland state, along with disease-carrying mosquitoes and the possibility of looting.

In St. George, which has a history of heavy floods, residents built levees, evacuated nursing home patients and set up a temporary hospital, with waters expected to peak early next week.

"Everyone is pitching in, doing what they can do," said Senator Barnaby Joyce, who lives in the town.

"As soon as this is over we have to concentrate on getting the show back on the road as quickly as possible, otherwise people will be out of work, the price of groceries will go through the roof."

Economists say the disaster could potentially shave about 0.5 percent off Australia's annual GDP growth, currently running at 2.7 percent.