The South Korean tried to raise a suspected North Korean submarine from the seabed yesterday, but defence ministry officials said none of the vessel's crew were likely to have survived.
"It is highly unlikely to see the North Korea crew come out of the sub alive," said Captain Oh Seyuong, who led the towing operations in the north-eastern port city of Donghae. "But we can not completely rule out the possibility of survival."
Ministry officials said the 25metre-long Yugo-class submarine, must surface two to three times a day to recharge its oxygen.
"The sub has not had a chance to recharge air since Monday afternoon. I don't think there will be survivors by the time now," said Major Kim Jung-woo, a spokesman for Seoul's joint chiefs of staff.
The navy attempted to bring the midget sub to a naval dockyard in Donghae by the end of the day. It sank on Tuesday while being towed to port by a South Korean warship.
"So far, all operations look okay," said Captain Oh, who hoped the submarine would be raised soon. Ministry officials said about 100 navy divers were working on the recovery operation.
Under the navy's plans, the sub would be moved onto land in the dockyard today for investigation, the ministry said.
The submarine sank in 30 metres of water on Tuesday, when a tow rope snapped about a kilometre from the dockyard. The sub can carry up to seven people.
A group suicide has not been ruled out. Military officials say North Korean infiltrators are trained to commit suicide to avoid capture. South Korea soldiers heard no response when they banged on the sub's hull.