Director of Marine Roger Tupper says a salvage operator has stablised the Ukrainian-registered tug that sank off Lantau Island on March 22, to prevent the wreck from further sinking.

The Ukrainian ambassador has arrived in Hong Kong to observe the rescue operation.

Speaking to reporters this afternoon Mr Tupper said although divers inspecting the wreck have so far seen no signs of life, the operation will continue until rescuers have retrieved the wreck and searched the vessel for the 18 missing crew members.

Hong Kong Island, Islands & Marine Commander Chief Fire Officer Chow Wing-tak said the salvage operator has decided not to move the wreck to shallow water because most of the vessel has settled into the seabed. Steel wires have instead been used to stablise the wreck to facilitate divers' work.

Although the rescue has been hindered by poor visibility due to silt and the rapid current in the area, Mr Chow said the salvage operator has used a recompression chamber to extend diving time.