An oil spill caused by a dredger boat hitting a stationary cargo tanker has blackened part of Singapore's southern coastline, including the popular resort island of Sentosa, and sparked concerns it may threaten marine wildlife as a cleanup operation was under way Sunday.

The Netherlands-flagged dredger Vox Maxima struck the Singaporean fuel supply ship Marine Honor on Friday. It damaged the cargo tank on Marine Honor, which leaked oil into the sea.

Singapore's Maritime and Port Authority said in a statement late Saturday the oil leak from the vessel had been contained, and that the oil that escaped from the damaged tanker had been treated with dispersants.

But due to the tidal current, it said the treated oil had landed along shorelines including at Sentosa and other southern islands, a nature reserve and a public beach park. Sentosa, which attracts millions of visitors annually, houses one of Singapore's two casinos, golf courses and Southeast Asia's only Universal Studios theme park.

Part of the beachfront at the public park and at the nature reserve have been closed to facilitate clean-up efforts, it said. The Sentosa beach will remain open to the public but sea activities and swimming are prohibited.

On Sunday, workers in orange suit were seen scooping up sand in a clean-up operation at an empty beach in Sentosa. Black water washed up on the oil-stained shore.

Authorities have deployed 18 crafts for the clean-up efforts and laid close to 1,500 meters of container booms, temporary floating barriers to trap the oil spill.

"More will be laid over the next few days to prevent further spread of oil onto the shore, and facilitate the recovery of the trapped oil off the affected shorelines and lagoons to prevent them from going back to sea," the statement said.

Conservationists and biologists are monitoring the full extent of the damage on marine and wildlife.

Local conservation group Marine Stewards reportedly said there were photos of dead fish, otters and kingfishers covered in oil slick.

Group founder Sue Ye told Singapore Straits Times that oil spills smother and suffocate fish, birds and marine animals that have to go to the surface for air, such as turtles and dolphins.