The 18 crew members were trapped 35 metres underwater in the boat which sunk after colliding with a freighter off Hong Kong in thick fog on Saturday night.
Divers said Sunday they had found the vessel on the seabed and had hammered on the hull of the tug boat but had so far received no indication that anyone on board had survived.
More than 130 people from fire, marine and other rescue departments were involved in Sunday's rescue operation, said fire services divisional commander Wong Chung-shing.
Wong refused to say if he believed any of the 18 might still be alive but said as long as there was air inside the sunken tug boat, there was a chance some might have survived.
The crew members were in cabins and inside the boiler room of the tug boat when it collided with a freighter between Hong Kong's Kowloon peninsula and Lantau Island at around 9 pm.
Six men and one woman on board the freighter, some of whom were thrown into the water by the collision, were rescued and taken to hospital during a night time rescue operation.
Divers and a government helicopter were brought in to aid the search for the sunken tug boat which was found 400 metres from the scene of the collision on the seabed.
If the 18 missing are confirmed dead, the incident will count as the worst single marine accident in Hong Kong's busy but closely regulated waters for decades.
Last Mod: 24 Mart 2008, 08:17