The Russian Sukhoi Superjet 100 at the international Paris Air Show in 2009. An SSJ 100 has gone missing over Indonesia in the middle of a demonstration flight.

A Russian passenger plane has gone missing over Indonesia, with at least 44 people onboard.

Indonesian authorities said it may have crashed into a mountain, according to Russian news agency RIA Novosti.

Radio and telephone contact have been lost, Russia Today reported.

The Sukhoi Superjet 100 took off from Jakarta's Halim Perdanakusuma Airport for a 50-minute demonstration flight over a mountainous area near Bogor, in West Java province, the Associated Press reported.

It disappeared from radar screens at an altitude of 6,200 feet, shortly after the pilot requested permission to descend from 10,000 feet to 6,000, RIA said. 

It is not clear why the crew changed course. According to the BBC, one eyewitness told local TV that he saw the plane "veering a bit to one side" and heading towards Mount Salak, which is 7,200 feet high. The witness said he did not hear an explosion.

Of those onboard, eight are Russians. The other 36 are believed to be Indonesians, most of them working for airlines considering buying the SSJ 100, according to RT.

Indonesia's national search and rescue agency has dispatched a team to the area.

"We are still looking for it and we are uncertain whether it crashed," spokesman Gagah Prakoso told Agence France Presse.

RIA cited Indonesian air traffic officials as saying the search operation is being hampered by bad weather and approaching nightfall.

The plane had enough fuel for four hours' flight, according to the BBC.

The medium-haul aircraft had already carried out another demonstration flight earlier in the day, RT said. It was on a tour of six Asian countries designed to show off its capacities to potential buyers.

"Before the second flight, the plane underwent required maintenance and was technically in good order," a spokeswoman for Russia's United Aircraft Corporation told RT.

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