Divers have been involved in a complex rescue operation
At least one person has died and eight are missing after a fishing boat sank during the search for a South Korean warship, officials say.
The South Korean boat was one of a number of private vessels searching for the warship, which sank last week near the maritime border with North Korea.
One official said the boat appeared to have collided with a freighter.
South Korea's Joint Chiefs of Staff said one of the 46 sailors missing from the warship was found on Saturday.
The fishing boat lost contact with the coastguard after sending a distress signal when it left the search area late on Friday.
"We've captured the Taiyo 1, a Cambodian-registered 1,472-ton freighter, which was apparently involved in the collision," an Incheon Maritime Police spokesman told AFP news agency.
If the fishing boat is confirmed to have sunk, it will add to the sense of shock that many South Koreans are feeling following the loss of the warship, the BBC's John Sudworth reports from the South Korean capital, Seoul.
He says the press is full of speculation about the possible causes of the explosion that sunk the Cheonan, including a deliberate attack by North Korea - a possibility not yet ruled out by the South.
Last week a navy diver was killed while taking part in the rescue operation.
The blast sunk the Cheonan, a 1,200-tonne corvette, after tearing it in half near Baengnyeong Island, close to the maritime border with North Korea.
Rescuers have been continuing their search for sailors missing on board the ship. Officials have said some people could have been trapped alive in watertight sections of the vessel.
On Friday, South Korea's defence minister renewed speculation a torpedo could have caused the blast that sank the ship.
Kim Tae-young, who had previously said a sea mine could have caused the blast, called it a "likely possibility" the Cheonan had been hit by a torpedo.
Shortly after the sinking, Seoul said it did not believe North Korea had fired on the ship.
Pyongyang has made no official comment about the incident.