A massive clean-up is underway after an oil spill in eastern Australia that authorities now fear is 10 times worse than first thought.  Officials in Queensland state have warned that toxic sludge coming from the cargo ship Pacific Adventurer is carcinogenic and is threatening wildlife and swimmers. 

The oil spill that started on Wednesday off Moreton Island now covers around 60 kilometers of southeast Queensland shoreline, including the popular Sunshine Coast region where nine beaches remain closed after being contaminated by tons of oil.

The oil leaked into the ocean after containers loaded with fertilizer fell off a freighter in rough seas and fractured the vessel's fuel tanks.

The crew initially reported 20,000 liters of oil escaped, but more than 10 times that amount is now thought to have washed ashore.

With the slick far worse than previously thought the environmental disaster has become a dominant issue ahead of a Queensland state election next weekend.

The state government has rejected claims it has been too slow to react to the crisis.

The conservative opposition leader Lawrence Springborg says the official response to the spill has been abysmal.

"This has been a debacle of extraordinary magnitude," he said.  "Denied it, said it was a light oil spill.  A dozen people with buckets and shovels was never going to do it.  The plan hadn't been activated.  The government was caught short."

Queensland premier Anna Bligh says a measured approach to the clean-up is most effective.

"I can understand that people think it's a good idea to get out there day one and start cleaning up," said Bligh.  "The reality is we still have oil coming onto the beach.  You don't take it all off the beach until you know it's all there, otherwise you are just stripping layer and layer and layer of sand off beaches that have already been eroded by cyclonic activity  

The owner of the freighter at the heart of the disaster could face fines of up to one million dollars if found guilty of violating environmental laws.

Authorities say the huge clean-up operation is about halfway through but it remains a difficult task.

On picturesque Moreton Island, more than 300 workers have been scraping black sludge off sand and rocks by hand.

Officials have warned that the toxic slick, one of Queensland's worst environmental disasters, is carcinogenic and poses threats to swimmers as well as wildlife.