The Malaysian authorities vowed today to track down the ship responsible for a huge oil spill off its southern coast which has caused serious damage and forced hundreds of fishermen to lay down their nets.

However, fishing groups criticised the slow pace of the clean-up and experts warned the spill could cause irreversible environmental damage to marine life.

"We are trying to identify the ship that spilled the oil," said Abdul Rahman Awang, director of the environment department in southern Johor state which lies opposite Singapore.

The busy shipping route was hit on Thursday by a five-kilometre long oil slick which left Johor beaches covered with tar balls and harbours full of black, oily water.

Some 200 fishermen in Pengerang, on the southernmost tip of Malaysia, have not been out to sea since Friday because they fear the oil slicks will damage their nets.

They also criticised local authorities for not carrying out immediate clean-up operations near the river mouth and on the beach, and said each boat was suffering daily losses of up to RM1,000.

Major disaster

Abu Bakar Mohamad, president of the Fishermens Association of Pengerang, told AFP that some 200 fishermen had been affected by the spill.

"It is a major disaster. We hope that whoever is responsible will be caught and be forced to pay compensation directly to the fishermen," he said.

"We hope the authorities will clean up the oil spill as soon as possible so that my members can feed their family," he added.

Fisherman Harun Salim said that because the oil sludge still covered the local Rengit river, most of the fishermen were still not able to go out to sea.

"The oil sludge will destroy our nets. The stain on the nets will drive the fish away," he said.

Vincent Chow, an environmental scientist with the Malaysian Nature Society in Johor, said oil slicks in the area were a common problem because it was located opposite one of the world's busiest ports - Singapore.

"There appears to be no contigency plans to tackle the oil spill and prevent it from hitting the coast. It is going to be an ecological disaster in the next few years," he said.

"The authorities must arrest the culprit. They must be punished so that it will be a lesson and deter others from committing the offence," he said.