An Asiana Airline cargo plane with two crew on board crashed Thursday into the sea off South Korea's Jeju island.

The Jeju Coast Guard said its patrol boat found debris of the Boeing-747 aircraft operated by South Korea's second-largest flagship carrier in the sea about 170 kilometers west of Jeju city.

The plane took off from Incheon International Airport at 3:05 am (local time) and was heading for Shanghai's Pudong airport.

An official from the Ministry of Land, Transport and Maritime Affairs said in a press briefing that the plane was believed to have caught fire in flight, but the exact cause of the crash could not be confirmed until the recovery of its flight data recorder.

He said the pilot told air traffic controllers in Shanghai that fire had broken out in the hold and that the plane was trying to make its way to Jeju airport.

The plane was carrying 58 tons of cargo, including semiconductors, machine parts and 0.4 ton of inflammable materials.

Five coast guard patrol boats and one helicopter are searching the area for the two crew including the captain, 52, and first officer, 44.

Asiana Airlines is the country's second-largest flagship carrier after Korean Air.