A new Russian passenger jet carrying 50 people has gone missing on a demonstration flight in Indonesia, after taking off from Jakarta.
The Sukhoi Superjet 100 disappeared from radar screens 50 minutes into what was meant to be a brief flight.
An eyewitness reported seeing a low-flying plane flying towards a mountain but did not hear any explosion.
Aerial searches for the plane have been hampered by darkness and strong winds.
But rescuers have continued looking for the plane on the ground.
"We suspect the plane crashed, but we're not yet certain," rescue chief Marsdya Daryatmo told reporters several hours after the disappearance.
Most of those aboard are believed to be Indonesian airline representatives but it has been confirmed that there are also eight Russians, including pilots and technicians, and a French citizen.
According to a manifest published by Russian news agency Ria-Novosti, which has not been confirmed, two Italians and a US citizen are also aboard the plane.
The jet vanished from radar near the city of Bogor in West Java province and may have come down in mountainous terrain around Mt Salak.
Relatives of Indonesians aboard the plane have gathered at the airport to wait for news, some of them weeping uncontrollably, AFP news agency reports.
The plane took off from east Jakarta's Halim Perdanakusuma airport at 14:00 (07:00 GMT), on its second flight of the day, the Indonesian search and rescue agency said.
At 14:50, it was recorded as dropping from 10,000ft [3,000m] to 6,000ft near Salak, a peak measuring 7,200ft (2,200m).
Juanda, a villager who lives near the mountain, told local TV: "I saw a big plane passing just over my house."
"It was veering a bit to one side, the engine roaring. It seemed to be heading toward Salak, but I didn't hear an explosion or anything."
Jocean Bowler, an American running an organic farm on the slopes of the mountain, which is a popular tourist destination, said: "Salak's a big mountain, I didn't hear anything."
Some 200 police, military and rescue workers have been sent to Mt Salak, Marsdya Daryatmo said.
Russian blogger Sergey Dolya, who was accompanying the Sukhoi delegation and broke news of the plane's disappearance, has been filing updates on Twitter, from the emergency operation centre in Jakarta.
"The ground [search] operation will continue all night," he wrote.
"They will try to climb to the highest point. In the morning, they will continue with five helicopters."
Tweeting after midnight (local time), Dolya added: "We keep phoning our guys. Sometimes calls go through, sometimes they break off. But nobody picks up. The locals are unable to determine the location."
Sukhoi officials have been on an Asia-wide tour in recent months to show off their aircraft to airline firms.
The Superjet, a mid-range airliner that can carry up to 100 people, is military plane-maker Sukhoi's first commercial aviation plane.
It was created by a joint venture, majority-owned by Sukhoi, with Italy's Finmeccanica and a number of other foreign and Russian firms also involved.
Sukhoi aimed to sell 42 of its planes to Indonesia, which has witnessed a fast-expanding aviation market to cater for a growing middle class in the world's fourth most populous nation, Reuters adds.