Rescuers are continuing their desperate attempt to reach 18 Ukrainian seamen trapped in a tugboat 37 metres under the sea since Saturday night but hold little hope they could have survived. Two days after the Neftegaz-67 sank after colliding with a freighter off Tuen Mun, Director of Marine Roger Tupper said there was no way of knowing if they were alive or dead. 'We haven't found any of the 18 seafarers during surface searches and the attempt to get a response from within the vessel has so far not received any response,' he said. 'Nevertheless, our operations are continuing. We are going to find a way to access the hull. We will continue until we have searched the inside.' Mr Tupper said experience showed that people trapped underwater, even if they had oxygen from an air pocket, could survive only about 12 hours at 17 degrees Celsius - the temperature at the wreck site. Chief fire officer Chow Wing-tak said the tug had sunk further into the seabed and it was not appropriate to try to pull it to shallow water. Two iron cables were fixed to the vessel late on Sunday to stabilise it and prevent it sinking further. A spokesman for the Guangzhou Salvage Bureau, which is helping to recover the vessel, said the Hua Tian Long, the biggest floating derrick in Asia, would arrive at the scene on Friday to help. The tugboat captain has been quoted as blaming those in charge of the 150-metre Chinese freighter Yaohai for the collision. Agence France-Presse reported Anatoly Prisiazhnyuk, president of the energy company Chornomornaftogaz, which owns the ship, saying that the captain had received permission from the controller to pass. 'The Chinese cargo ship should have let it pass, but it did not do that,' Mr Prisiazhnyuk said from Simferopol in Ukraine. Ukraine's ambassador to Beijing, Serhiy Kamyshev, arrived in Hong Kong yesterday. He said his government had set up a special commission under the prime minister to handle the crisis.