Indonesia focused rescue efforts on Sulawesi island today after an Adam Air Boeing 737-400 plane went missing yesterday with 96 passengers and six crew on board.

The plane lost contact with the ground about an hour before it was due to land in Manado in North Sulawesi, Tatang Ikhsan, director general at the transport ministry, said. It had been flying at 10,670 metres.

An official said efforts to reach the co-pilot by mobile telephone indicated the plane was on the ground rather than in the sea, where the telephone would be unlikely to work.

"There was a ring tone, but no answer," said Abdul Gani, a Search and Rescue duty officer at Makassar, capital of the region from where a distress signal was picked up by satellite.

Speaking to Reuters by telephone, Mr Gani said the signal indicated the plane might be in a mountainous area. Air and sea searches would begin in the morning, he said.

Mr Ikhsan said the flight had originated in Jakarta, taken off from a stopover in Surabaya on Java island at 1 p.m. (0600 GMT) and been scheduled to land just over two hours later in Manado.

At a news conference late yesterday he said the satellite, in Singapore, had dectected the distress signal 154 km northwest of Makassar, the capital of South Sulawesi province, 1,400 km east of Jakarta.

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

Transport Minister Hatta Rajasa said the plane had been sighted by another plane above the Mamuju forest on Sulawesi.

"Let's hope it made an emergency landing," he told Elshinta radio, adding that rescuers had been sent to the area.

At Jakarta's main commercial airport, where the flight began its journey, taxi driver Oswald Mamalani said his younger sister and her child were aboard the plane.

"When I arrived home, I got a phone call from a relative in Manado asking me to pray... for the safety of my sister," he said. "So far I feel that my sister is still alive."

First Marshal Eddy Suyanto, commander of Hasanuddin air base in Makassar, told Metro television: "We have contacted related agencies and several groups have travelled by road to locations where we think the plane might have gone down but so far there has not been any information."