Asiana Airlines cargo plane crashes off the coast of South Korea's Jeju Island [Reuters]

A cargo plane has crashed off the coast of South Korea's southern Jeju island.

According to unconfirmed local media reports, searchers found sea wreckage of an Asiana Airlines cargo plane that crashed on Thursday.

The plane is thought to have had two occupants, a pilot and co-pilot aboard.

Choi Kyu-mo, the Jeju island coast guard's spokesperson said four ships and a helicopter were searching the wreckage west of the southern resort island of Jej.

Yonhap News Agency earlier cited the coast guard as saying one of its patrol boats had found debris from the aircraft operated by Asiana, South Korea's second-largest flagship carrier, in waters about 107km west of Jeju city.

The plane had reportedly left from South Korea's Incheon International Airport and was bound for Pudong in China.

'Mechanical difficulties'

Asiana officials got a report early on Thursday from the pilot that the Boeing-747, which was southwest of Jeju, was having mechanical difficulties and would try to make its way to the island's airport, Jason
Kim, a spokesman for Asiana Airlines, said.

Officials then lost contact with the plane and asked the coast guard to investigate, Kim said.

The airline also sent its own emergency specialists to the area.

Kim said he had seen media reports about the crash but was waiting for a final investigative report from the coast guard and Asiana airline officials at the site before confirming anything.

South Korea has been lashed with extraordinarily heavy rain this week, with landslides and floods killing dozens and causing havoc.

Kim said it was unclear whether the weather had caused any problems for the plane.

Kyu-mo said there was no rain in the area but that there were stronger-than-normal winds at the time.

Source: Agencies