Divers on Friday resumed their search of a South Korean warship that sank near the tense North Korean border after two days of bad weather halted the operation, as the cause of last week's sinking remained a mystery.
High waves and strong currents had put a stop on the search for the 46 crewmen, who have been missing since their ship broke in two after an explosion, causing anguish among families still hoping for a miracle.
The 1,200-tonne corvette went down on the night of March 26. Fifty-eight crewmen were saved at the scene.
Most of the rest were thought trapped in the stern section, but divers as of Friday morning had been unable to get into all the cabins or other rooms.
"It is very hard to say when we will be able to find the missing," military spokesman Lee Ki-Shik told a briefing. "Our rescuers are still trying to get in despite the bad weather, so please be patient."
No one has officially declared them to be dead, even though the air in any watertight compartments would long since have been used up.
Authorities are also desperate for clues to the cause of the disaster although these may not emerge until the hull sections are lifted from the Yellow Sea. A private salvage ship is at the scene.
The disputed border was the scene of deadly naval clashes between North and South Korea in 1999 and 2002 and of a firefight last November.
Seoul has ordered its military on alert but not cited any evidence the North was involved. The defence minister has said a North Korean mine -- either drifting or deliberately placed -- might have caused the disaster.
However, his ministry has said it was very unlikely that the North's submarines had penetrated close to the Cheonan warship at the time.
A 60-member investigation team of military and civilian experts is being formed.
President Lee Myung-Bak has ordered the military and civil service on heightened alert but appealed Friday for people not to overreact.
"North Korea and the international community are watching. We should look into the case in a calm manner and use it as a chance to elevate national capability," he said.