The Hong Kong authorities have mobilized over 130 rescuers to continue searching for the missing 18 Ukrainian seamen after a boat collision Saturday night, a marine official said on Sunday.

Roger Tupper, Director of Marine, told a press conference that rescuers from marine and flying services failed to find any survivors on the sea surface and the 18 missing seamen were believed to remain inside the cabin of their 80-meter-long tugboat, which sank and capsized at the seabed about 35 meters underwater.

The accident occurred near the Brothers, an island group located between Tuen Mun and the Hong Kong International Airport, at around 1330 GMT Saturday when "Yao Hai," a 150-meter-long container-carrying freighter registered on the Chinese mainland, and the Ukrainian-flag hanging tugboat bumped into one another.

The tugboat, the smaller vessel, was heading towards an oilfield in the South China Sea and carrying 24 Ukrainians and one Chinese on board when the accident occurred.

It sank shortly after the collision as its seamen on board were either thrown into the water and trapped inside its cabin by the force of the collision.

Tupper said the first rescue vessel from the marine police arrived at the scene four minutes after the marine department received the SOS signal.

Seven seamen, one Chinese and six Ukrainians, were rescued from the sea surface while others on the tugboat were still missing. Meanwhile all the 25 seamen boarding the larger freighter, which was sailing towards Tsuen Wan in eastern Kowloon, were safe.

Tupper said the Department of Marine had informed the Ukraine Embassy in Beijing on the accident and the department were willing to provide information to the families of those missing seamen.

Chow Wing-tak, Chief Fire Officer of Hong Kong Command, said at the press conference that the frogmen had dived underwater for many times after they located the sunk boat at around 4:00 o'clock (2000 GMT) on Sunday morning.

"They knocked at the hull of the boat but had no response," Chow said, adding the frogmen failed to find one of the only two entrances of the capsized boat amid mud and low visibility.

"Each frogman could only hold for 20 minutes 35 meters underwater due to the swift torrent and the low visibility," Chow said, "such conditions added to the difficulty of rescue.

Chow said a crane vessel had been summoned to the scene to pull the sunk boat to a shallower water to let those frogmen to have more time searching for the missing Ukrainians.

Tupper said the Department of Marine were still investigating the cause of accident and any possibility can not be ruled out.

The Marine Department had warned ships sailing on Hong Kong's waters on Saturday morning that visibility was as low as 740 meters.

Six years ago, a collision off Ma Wan between a dredger and a container left eight people dead in Hong Kong.

(Xinhua News Agency March 24, 2008)