SEOUL, South Korea (AP) – Coast guard boats and helicopters searched today for 14 sailors feared dead in chilly waters off South Korea after their cargo ship was thought to have sunk in high seas.

The ship, carrying 2,000 tons of nitric acid, went missing after it sent out a distress signal early Tuesday off Yeosu, 280 miles south of Seoul. One sailor was rescued but the remaining 14 crew members had yet to be located.

“Unfortunately, we didn’t find any survivors,” coast guard spokesman Kang Byung-mun said after overnight search and rescue works. “We believe the ship sank.”

The nitric acid on board was not likely to cause environmental damage because it easily dilutes, officials said.

No wreckage has been found yet, Kang said.

The coast guard has found 18 drum cans and several life jackets and boats believed to be from the ship, he said. The survivor – a 28-year-old Burmese – told investigators he watched the vessel sink before he and the other crew members – 12 South Koreans and two Burmese – were swept away, Kang said.

A total of 34 ships, three helicopters and one aircraft were to continue searching Wednesday, he said.

The coast guard also planned to dispatch boats to measure the acidity of the water to determine whether or how much nitric acid was released, said an officer at the coast guard’s marine pollution bureau.

“Even though the ship has already sunk, the nitric acid will likely be kept in the ship’s storage facilities, which have good safety devices,” the official said on condition of anonymity, citing a bureau policy.

The news comes as South Korea battles to contain its worst-ever oil spill, which has blackened beaches and jeopardized the ecosystem along the country’s west coast. A wayward barge hit a supertanker on Dec. 7 causing the tanker to leak 78,920 barrels of oil.