Indonesia's search and rescue agency said radio contact with the plane was lost at about 0800 GMT after the jet descended to 6,000 feet around Mount Salak, a volcano 2,211 metres (7,254 feet) above sea level south of the capital Jakarta.

The Superjet 100 plane - Russia's first all-new passenger jet since the fall of the Soviet Union - was carrying Indonesian businessmen, Russian embassy officials and journalists, and a search by helicopter and land had so far not found it, Indonesian and Russian officials said.

Transport ministry spokesman Bambang Ervan said the plane was flying at 10,000 feet and asked for permission to descend to 6,000 feet. "The last contact was when they asked for permission to descend from 10,000 feet to 6,000 feet," Ervan said.

"The plane was doing the first flight around midday and returned to the airport, but when it took off the second time, it lost contact around Bogor," Ervan said.

There were eight Russians on board, including pilots and technicians, said Dmitry Solodov from the Russian Embassy in Jakarta. The search and rescue agency earlier said there were 46 people on board.

"The search operation, by chopper and on the ground, has not found the plane until now," said Solodov.

The country's search and rescue agency is looking for the jet near one of many volcanoes that form the backbone of Indonesia's main island.

"Salak's a big mountain, I didn't hear anything," said Jocean Bowler, an American running an organic farm on the slopes of the mountain, visible from the capital on clear days and a popular tourist destination.

Olga Kayukova, a spokeswoman for Russia's United Aircraft Corporation, told Reuters the Sukhoi Superjet-100 was on a second flight as part of a demonstration programme in Indonesia.

"The first flight was carried out in a normal mode ... The pre-flight preparations were carried out in full and the plane was completely ready to fly," she said.

"According to information from Indonesia, the contact with the plane was broken after 20 minutes from the take-off, at 1435 local time," Kayukova said.

Air traffic accidents are common in Indonesia, a sprawling Southeast Asian archipelago of 17,000 islands.

Sukhoi, which has orders for 170 planes worldwide, plans to produce up to 1,000 superjets, primarily for foreign markets. It aimed to sell 42 planes to Indonesia, which is seeing a fast expanding aviation market to tap travel by a growing middle class in the world's fourth most populous nation.

The jet was developed with Western design advice and technology from Boeing (BA.N) and Italy's Finmeccanica (SIFI.MI), as well as avionics and engine equipment from French aerospace firms Thales (TCFP.PA) and Safran (SAF.PA).

Built in a converted corner of a Sukhoi fighter factory in Siberia, it was first unveiled in 2007 as part of a drive to curb Russia's dependence on oil and gas and restore pride in its aviation industry, but ran into a series of development delays.

The Superjet 100, with a capacity of 68-103 passengers, is already in service with Russia's Aeroflot and Armenian carrier Armavia and is half way through a 15,500-km (9,630-mile), six-nation Asian tour to try to drum up more international customers.

The aircraft is being marketed internationally in partnership with Finmeccanica subsidiary Alenia Aeronautica.

(Additional reporting by Heru Asprihanto and Fergus Jensen in Jakarta, Vladimir Soldatkin and Gleb Stolyarov in Moscow; Writing by Neil Chatterjee; Editing by Louise Ireland)

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