None has been found since an initial rescue of 58 sailors from the 1,200-ton Cheonan that sank early on Saturday near the tense border with North Korea. No bodies have been discovered.
The ship was on a routine patrol with other vessels in the Yellow Sea off South Korea's west coast. The exact cause of the explosion remained unclear and officials said it could take weeks to determine.
It is one of South Korea's worst naval disasters. In 1974, a ship sank off the south-east coast in stormy weather, killing 159 sailors and coast guard personnel. In 1967, 39 sailors were killed by North Korean artillery.
Fierce waves and high winds have hampered the search in the area where the two Koreas have fought bloody naval engagements. Despite the location of the sinking, North Korea did not appear to be involved.
General Walter Sharp, chief of the 28,500 US troops in South Korea, said: "We have detected no special movements by North Korean forces, however, we, as a command, continue to monitor the situation and remain prepared for any contingency."
South Korean troops were maintaining "solid military readiness", the Defence Ministry said.
The Cheonan sank about a mile from Baengnyeong Island, which is about 10 miles from North Korea. The Koreas remain in a state of war because their three-year conflict ended in a truce, not a peace treaty, in 1953.
The explosion tore open the rear hull of the Cheonan, shut down its engine, wiped out power and caused the ship to sink a little over three hours later. The ship then broke into two pieces, officials said.
Military and coast guard ships and helicopters were searching the chilly waters yesterday.
Rescue ships retrieved about 20 life jackets and 15 safety helmets in waters seven to 18 miles away from the site, Joint Chiefs of Staff spokesman Park Seong-woo said.
The weather conditions had improved from Saturday, but Yonhap news agency said dozens of military divers quickly withdrew due to rapid sea currents.
As hopes faded for the missing crew, about 80 family members aboard a navy patrol boat sailed around the site.
"My son! My son!" one crying woman shouted while boarding the ship at a naval base south of Seoul for the journey to the accident area as other relatives wailed in grief.
Some families also vented anger at the military, accusing authorities of a cover-up and saying survivors told them the Cheonan was leaky and in need of repair. They shouted "Liars!" and jumped on a car carrying the rescued ship captain as it drove away.
As family members scuffled with guards, some soldiers pointed their guns at the protesting relatives.
"I find this gruesome reality – one where soldiers point their guns at heartstricken families of their comrades in arms – absolutely devastating and regrettable," said Chung Hae-kyung, 65, father of a missing lieutenant.