(CNN) — An oil spill affecting Singapore has spread beyond a luxury beach resort to a marine reserve and other parts of the island nation as authorities intensify cleanup efforts.

The oil spilled into the city-state’s waters after a Netherlands-flagged dredger, Vox Maxima, hit Singapore-flagged bunker vessel, Marine Honor, on Friday afternoon, according to the Maritime and Port Authority of Singapore (MPA).

While the oil leak from the vessel had been contained and treated with dispersants as of Saturday, some of the treated fuel had spread due to the tidal currents, according to the MPA.

The oil spill has spread from the busy Pasir Panjang Terminal cargo port, less than 10 kilometers (6 miles) from Sentosa, the country’s popular resort island home to luxury hotels, golf courses and Universal Studios Singapore.

The incident occurred at the start of the Hari Raya Haji long holiday weekend, during which locals and tourists alike were expected to flock to Sentosa and other landmarks.

While the scale of environmental damage of the spill remains unclear, local conservation group Marine Stewards posted photos of oil-soaked birds and shorelines on its Facebook page.

“There have been many cases of wildlife affected — a number of kingfishers, otters and monitor lizards covered in oil, seabirds whose legs are stained with oil. We have also received reports of dead fish and a dead sea snake,” said Marine Stewards founder Sue Ye in a statement.

Workers clear the oil slick in plastic bags on Sentosa island's Tanjong Beach in Singapore on June 16. (Photo credit: Roslan Rahman/AFP/Getty Images via CNN Newsource)

Cleanup efforts were ongoing Monday with about 100 workers deployed across Sentosa’s beaches, a spokesperson from the Sentosa Development Corporation (SDC) told CNN.

Sentosa’s beaches remain open to the public but swimming and water activities are not allowed at Tanjong, Palawan and Siloso beaches on the west coast of the island, the SDC added.

The outlying islands of St. John’s, Lazarus and Kusu were closed off on Sunday evening as the slick had spread to the shores of the first two locations, which are popular among day trippers via ferries and yacht charters, according to a joint statement from the National Parks Board, together with scientists and volunteers from Friends of Marine Park.

Authorities deployed skimmer vessels for the cleanup efforts and laid close to 1,500 meters (4,921 feet) of oil absorbent booms to protect a coastal natural reserve lined with mangroves.

Singapore is a global shipping and fuel bunkering hub that sits along a narrow, busy strait connecting the Indian Ocean with the South China Sea. Measuring about 13 kilometers (8 miles) long, 19 kilometers (11.8 miles) wide and dotted with several small islands, it is one of the world’s busiest commercial waterways where around 1,000 ships pass through every day.

Heng Kiah Chun, regional campaign strategist for Greenpeace, said the incident was a “wake-up call” on the need to phase out fossil fuels that bring permanent harm to people and the planet.

“The oil spill is a growing environmental catastrophe that is impacting some of the region’s most important and biodiverse marine protected areas and fisheries areas,” Heng said.

This story has been updated with additional information.

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