A rescue operation is underway in Hong Kong waters, as eighteen Ukrainian sailors are trapped underwater after their tugboat sank off following a collision with a cargo ship.

Ukrainian President Viktor Yushchenko has urged the government to take all measures to rescue the missing sailors.

Director of Marine Department, Roger Tupper says the sailors may still be alive.

"Much of the effort now of course is to try and get inside that wreck. We have to get the vessel to shallower water to enable the divers to have a better environment to operate in, and also to try, because the vessel is upside down on the seabed, to try and move the vessel so as we can get some access into the vessel."

The Ukrainian tugboat Neftegaz, which was on its way to an oil field south of Hong Kong, collided with Chinese-registered cargo ship Yao Hai late on Saturday in waters northwest of Hong Kong's outlying Lantau island.

Seven members have been reportedly rescued and efforts were continuing to find the other missing Ukrainian citizens. All of the crew members aboard the Chinese cargo ship have been rescued.

According to the marine official, the cause of the accident is not yet known and that weather conditions are reasonable at the time it occurred.