Contact with air traffic control was lost when the plane was at an altitude of 35,000 feet, about one hour before it was due to land, an official said.

   

He later told a news conference that a Singapore satellite picked up a distress signal from a plane 83 nautical miles northwest of Makassar, the capital of South Sulawesi province.

   

"We call on other flights which crossed this route to provide information on any distress signal," he said.

   

Sighted

 

Rajasa said the plane had been sighted above the Mamuju forest on Sulawesi.

   

"[It was] preliminary information from a plane flying above it. It will be the first clue for SAR [Search and Rescue] to move to the area," he told Elshinta radio, adding that rescuers had already been ordered to go.

   

"Let's hope it made an emergency landing," he said.

   

An Adam Air Boeing 737-300 plane was forced to make an emergency landing in February at a small airport in East Nusa Tenggara province after a navigational failure caused the pilot to lose contact with the destination airport in Makassar.

   

Adam Air, one of about a dozen budget airlines in the world's fourth most populous nation, operates 19 Boeing 737 jets. It serves dozens of domestic routes in Indonesia and also flies to Singapore.

   

It commenced operations in December 2003.

   

Air travel in Indonesia, home to 220 million people, has grown substantially since the liberalisation of the airline industry after the Asian financial crisis in the late 1990s.