Both pilots aboard a China-bound Boeing 747 cargo jet were killed when it crashed off South Korea after experiencing mechanical problems.

The plane, which was flying for South Korea's Asiana Airlines, came down off Jeju island in the very south of the country, local media report.

It had left Incheon en route to Pudong in China.

A South Korean coast guard boat found debris from the jet in waters about 107km (66 miles) west of Jeju city.

After taking off at 03:05 a.m. (18:00 p.m. GMT) the plane disappeared from radar at 04:09 a.m. while trying to reach Jeju airport, the South Korean news agency Yonhap reports. The wreckage was spotted at 06:40 a.m.

Both the pilot and co-pilot were killed.

Heavy rain has lashed South Korea this week, with landslides and floods killing dozens and causing havoc, but Asiana Airlines said it was unclear whether the weather had caused any problems for the plane.

The 747, nicknamed the Jumbo Jet, has been in service around the world for more than four decades, and is still in production.

Photograph: Debris was found at sea after the Asiana Airlines plane went down. Photo/Reuters