SEOUL (AFP) - South Korean prosecutors said Monday they had detained four more crew members in a widening investigation into a ferry disaster that left hundreds missing, presumed dead.

Three officers and one engineer from the capsized ferry Sewol were taken into police custody, a prosecutor on the case told AFP, following the arrest at the weekend of the captain and two other crew members.

The 6,825-tonne ship sank off the southwest coast on Wednesday with 476 people on board - mostly high school students on a holiday trip.

Captain Lee Joon-Seok Lee was arrested on Saturday along with a helmsman and the ship's relatively inexperienced third officer, who was in charge of the bridge when the ship first ran into trouble.

They were charged on counts ranging from criminal negligence to violation of maritime law.

The four detained Monday could face similar charges, the prosecutor said.