Rescue teams were searching Thursday for six crewmembers missing after their oil-laden freighter collided with a chemical tanker in the Strait of Singapore, as Indonesian authorities announced that fuel found at the site was being tested.

Col. Ribut Eko Suryatno, commander of the Batam island marine base, told the Tribun Batam newspaper that oil from the Thorco Cloud had been sited in the waters of the Singapore Strait.

"We have taken a sample of the oil," he said of the navy’s efforts to determine the level of sea pollution.

Commissioner Police Hero Hendrianto Bakhtiar, director of sea and air police for the Riau Islands region, told Detik.com, "six lost crew members are still being sought by the navy and the Search and Rescue Agency.”

Bakhtiar said the Thorco Cloud freighter, which was carrying 560 metric tons of bunker fuel, was hit by chemical tanker Stolt Commitment while sailing from Singapore to Taiwan in the busiest commercial shipping route between Riau Islands and Singapore.

Six of the 12 crewmembers have been rescued by the Maritime and Port Authority of Singapore since the accident occurred at 08.30 p.m. (1330GMT) Wednesday around 11 kilometers (6.8 miles) northwest of Batam island.

Six of the total 12 crew could be saved by the Maritime and Port Authority of Singapore and transported to a hospital in the country.

The Indonesian navy has deployed three ships to help regulate maritime traffic at the site of the collision.

As of Thursday afternoon, only the tip of the crane used in moving cargo was visible from the body of the Thorco Cloud.