Search and rescue teams were heading to the area just south of the capital, said Bambang Ervan, a spokesman for the Ministry of Transportation. Bad weather, however, forced at least two helicopters to turn back.
The Sukhoi Superjet 100 took off from Jakarta's Halim Perdanakusuma Airport at 2:21 p.m. local time.
It dropped off the radar 21 minutes later near the Salak mountain range, after the crew asked air traffic control for permission to descend from 10,000 feet to 6,000 feet.
No explanation was given for the sudden change of course. Though drizzling at the time, it was not stormy.
"I saw a big plane passing just over my house," Juanda, a villager who lives near the 7,200-foot mountain, told the local station TVOne.
"It was veering a bit to one side, the engine roaring," she said. "It seemed to be heading toward Salak, but I didn't hear an explosion or anything."
Rear Marshal Daryatmo, chief of the national search and rescue agency, said several diplomats from the Russian Embassy, potential buyers from major Indonesian airlines and journalists were on board what was supposed to be a 50-minute demonstration flight — the second of the day.
Together with the Russian crew, the plane was carrying 50 people, said Sunaryo, from PT Trimarga Rekatama, the company that was responsible for the guest list. (Like many Indonesians, both Sunaryo and Daryatmo use only one name.)
Though the air search was called off by early evening, soldiers, police and members of the air force had joined the land-based rescue efforts. They were expected to continue through the night, but the terrain was rough and difficult to navigate after darkness fell.
"Hopefully they'll be able to reach the location tonight," Daryatmo said.
Developed by the Russian aerospace company Sukhoi in co-operation with Western partners, the plane is the first completely new airliner designed by Russia since the Soviet collapse.
Russia has hoped that the short- to mid-range jet, which made its maiden run in 2008, would help it break into international markets dominated by Boeing and Airbus.
It was on the fourth stop of a six-nation "Welcome Asia!" road show, after Myanmar, Pakistan and Kazakhstan. It was supposed to head next to Laos and Vietnam.
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