HONG KONG, March 23 - Eighteen Ukrainian sailors were trapped underwater Sunday in their capsized tugboat after it collided with a cargo ship in Hong Kong waters.

Hong Kong Director of Marine Dept. Roger Tupper was quoted by news services as saying the sailors were trapped in the ship's hull and could still be alive if they found an air pocket inside the vessel. However, he said rescue divers knocked on the boat and did not hear the sailors signal back.

The sailors were believed to be trapped inside the engine room and the cabins of the boat, which was lying capsized at a depth of 35 meters on the seabed, RTHK radio quoted Wong Chung-shing, a Fire Services divisional commander, as saying.

The commander declined to speculate if the crew members might still be alive, but said as long as the ship had air inside, the sailors had a chance.

Divers had made nine attempts to rescue the trapped sailors but were hindered by strong currents and poor visibility, the Hong Kong government said in a statement.

Rescuers were trying to move the 264-foot-long Ukrainian boat — which was upside down at a depth of 115 feet — to a shallower spot to ease rescue efforts, Tupper said.

"We have to get the vessel to shallow water to enable divers to have a better environment to operate," he said at a news conference. "That does take time. That's very unfortunate."

The Ukrainian tugboat Naftogaz, which had been traveling from the southern Chinese city of Shenzhen to an oil field south of Hong Kong, collided with Chinese-registered cargo ship Yao Hai late Saturday off Hong Kong's outlying island of Lantau, Tupper said.

He said six Ukrainians and a Chinese citizen were rescued from the tugboat and efforts were continuing to find the others.

The ships collided at around 9 p.m. on Saturday, but divers were only sent to look for the vessel four hours later because they could not find the ship at the location given by marine police, Reuters reported. It was possible the vessel had been swept along by strong currents while it was sinking.

Tupper said that the cause of the accident was not yet known and that weather conditions were "reasonable" when it occurred. Neither vessel was overloaded, he said.

All 25 crew members aboard the Chinese cargo ship were rescued, Tupper said.

The cargo ship suffered some damage but did not sink, the government statement said. (fx/ez)