A ferry sent distress call in waters off Jindo, South Jeolla Province on Wednesday morning.
The ferry left Incheon at around 9:00 p.m. on Tuesday and was heading to the southern resort island of Jeju, carrying over 470 passengers including 325 youngsters on a school trip.
Around two hours after the ferry suddenly started to sink at around 8:55 a.m. on Wednesday, 190 passengers had been rescued.
As of 11:00 a.m., the ferry was about to go under completely, with most of the passengers believed rescued. The ferry has a capacity of some 900 passengers and had enough life jackets.
The Coast Guard has dispatched over 20 patrol boats and aircraft to the scene. The Navy joined the rescue operations by sending a guided-missile patrol killer, six speed boats and a Lynx helicopter.
Why the ferry sank is unclear.