Eighteen Ukrainian sailors were trapped underwater in their capsized tugboat after it collided with a cargo ship in Hong Kong waters, a marine official said Sunday. Director of Marine Dept. Roger Tupper said the sailors might still be alive if they found an air pocket inside their vessel. He said, however, that rescue divers have knocked on the boat but have not heard the sailors signal back. The Ukrainian tugboat, which was on its way to an oil field south of Hong Kong, collided with a Chinese-registered cargo ship late Saturday in Hong Kong waters, Tupper said. He said six Ukrainians and a Chinese citizen have been rescued from the tugboat and efforts were continuing to find the others.