A ship carrying North Korean sailors has sunk off South Korea, killing at least two people.

Sixteen sailors were on board the Mongolian-flagged cargo ship that went down off the southern coast of South Korea.

Three of the crew have been rescued, South Korean officials said. A search was under way for the remaining 11 crew members.

The vessel was heading from North Korea to China with a cargo of steel.

South Korea’s coast guard said 13 vessels and six aircraft were involved in the search.

It is not clear what caused the ship, which sent a distress call in the early hours of Friday, to sink.

South Korea generally returns North Korean sailors who encounter trouble in its waters, if they want to return.