Baengnyeong Island: Weeping, angry relatives of 46 crew members missing after a mysterious explosion sank a South Korean navy ship sailed around the site today as rescue teams tooked to the air and sea still hoping to find survivors.

None has been found since an initial rescue of 58 sailors from the 1,200-ton Cheonan that sank early yesterday 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 southeast 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.

"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," Gen Walter Sharp, chief of the 28,500 US troops in South Korea, said in a statement today.

South Korean troops were maintaining "solid military readiness," the Defence Ministry said. It also said a US military ship would join rescue operations tomorrow.

The Cheonan sank about 1.8 km from Baengnyeong Island, which is about 17 km from North Korea.

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, Defence Ministry officials said today.

Military, coast guard ships and helicopters were searching the chilly waters today. As hopes faded for the missing crew, about 80 family members aboard a navy patrol boat sailed around the site and watched rescue operations. "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.