A Russian passenger jet vanished from radar screens and is feared to have crashed in Indonesia where it was on a test flight.

The Russian-made Sukhoi Superjet-100 was carrying about 50 people when it vanished from radar screens shortly after the pilot requested permission to descend from 10,000 feet to 6,000 feet. The Russian news agency  RIA Novasti reports the plane was last seen turning toward a tall mountain range south of Jakarta.

A Russian blogger in Jakarta reports that an American was among those on board.

Olga Kayukova, a spokeswoman for the United Aircraft Corporation which owns Sukhoi,  said in a statement posted on Facebook that the plane had been checked properly prior to take-off. She confirmed that air traffic control lost contact with the plane about 20 minutes into the flight.

"We are carrying out search operations, set up operational headquarters," she wrote.

According to the Russian blogger, search operations began using helicopters but had to turn back due to bad weather. A search party has set out on land, but has not yet found the plane. Relatives of the passengers have gathered at the Halim military air base in Jakarta, anxiously awaiting news.

The plane was part of a pair that were reportedly on a six country swing through Asia where it was being demonstrated for potential customers including government and military officials. They had already been to Myanmar, Pakistan and Kazakhstan. They were to travel to Laos and Vietnam next.

Kayukova, the United Aircraft Corporation spokeswoman, said in her statement that the first plane flew without problems earlier in the day.

The Russian blogger, Sergei Dolya, was traveling with the Sukhoi delegation on the Asia trip but decided not to take the flight. He said relatives of those on board tried to reach them by phone, but were unable to get through.  On his blog he wrote that he did not have any update on the status of the plane.

He wrote that the plane was carrying 36 foreigners and eight Russians when it disappeared. RIA Novasti, which also had a reporter on the promotional trip, reported that representatives from several Indonesian airlines were among those on board.

If the jet crashed it would be the latest in a string of accidents for the Russian aviation industry which last year earned Russian the dubious title of most dangerous country in the world to board an airplane.

ABC News' Dada Jovanovic and the Associated Press contributed to this report