A Malaysian cargo plane made an emergency landing in western Japan today after its captain fell unconscious on a flight from the United States to Hong Kong, the Japanese transport ministry said.

The McDonnell Douglas MD-11, flying from Anchorage, Alaska and operated by Transmile Air Services, was travelling at an altitude of about 11,600 meters over Kochi, western Japan, at about 11:45am (0245 GMT) when the captain fell sick.

"He suffered a convulsion and lost consciousness," said Hiroshi Oda of the ministry's civil aviation bureau.

The captain, whose identity was withheld, regained consciousness after the plane landed at Kansai International Airport in Osaka, the official added. "He was taken to hospital and his condition was reported to be stable."

There were five people on board - the captain, two pilots and two airline employees.

The captain was in the co-pilot's seat when he fell ill but it was not immediately clear who was controlling the plane. He was immediately replaced by a standby pilot, Oda said.

"The ministry is investigating the case as a 'serious incident' which could have led to an accident," he said.