A Russian Sukhoi Superjet 100 on a demonstration flight with about 50 people on board is missing south of the Indonesian capital, Jakarta, according to Indonesian search and rescue officials.
The airliner was on a demonstration flight for potential buyers when it disappeared off the radar on Wednesday.
"We suspect the plane crashed, but we're not yet certain," rescue chief Marsdya Daryatmo told reporters.
"We tried to send two helicopters to search for the plane ... but because of bad weather and strong winds they had to return."
By midnight, hundreds of rescuers had set up three posts around the mountain.
"We arrived here very late at night, and we plan to set out at dawn. Others are already searching by foot," Joshua Banjarnahor, a rescuer at a post set up at Cidahu town, told the news agency AFP.
"There are hundreds taking part in the search and helicopters will again go out Thursday at sunrise."
The aircraft was carrying Indonesian businessmen and Russian embassy officials, the transport ministry said. Journalists were also on board.
The jet, made by the Russian company Sukhoi, radioed a distress message before disappearing. The Ria Novosti news agency said there were at least eight Russians among the passengers.
Al Jazeera's Step Vaessen, reporting from Jakarta, said: "The flight should have lasted just 30 minutes in the area around Jakarta, but it never returned.
"They [ground control] lost contact after the Russian pilot asked to descend from 10,000 feet [3,000m] to 6,000 feet [1,800m] and then they never heard from the plane again.
|Distraught relatives of passenger waited for news about
the plane at Jakarta Airport [Reuters]
"This was a brand new plane from Russia. It came into the country just yesterday and took people on board for an earlier test flight this morning. That all went well."
Relatives of passengers gathered at Jakarta Airport after the disappearance, waiting for information about the missing plane.
Yanny Mariana's eyes welled up with tears as she told reporters that one of her four friends on the flight had called her in panic.
He had earlier told her the plane would fly above the city of Bandung and be back in Jakarta in under an hour.
"But at around 3:00 pm (08:00 GMT) he called me in a panic and I was worried because I knew it shouldn't take that long to fly to Bandung and back," she said.
The Sukhoi Superjet 100 is a new passenger plane built in Russia in a bid to lift its civil aviation industry from a post-Soviet crisis.
The plane is considered crucial to Russia's hopes of becoming a major player in the modern aviation market and improving the image of an industry scarred by frequent crashes of ageing Soviet-era jets.
The demonstration flight in Indonesia was part of a tour dubbed the "Asian Roadshow" aimed at promoting the aircraft abroad that started May 3 and earlier took in Kazakhstan and Pakistan. It was due to go on to Laos and Vietnam.
In August last year, Indonesian regional carrier PT Sky Aviation agreed to buy 12 of the planes, with deliveries due to begin in 2012.
The Superjet project is a joint venture between Sukhoi and Italy's Alenia Aeronautica, which is part of the aerospace and defence giant Finmeccanica.
Alenia owns 25 per cent plus one share of Sukhoi Civil Aircraft, the Sukhoi unit developing the jet, as well as 51 per cent of Superjet International, which is handling sales of the aircraft.
However the plane has experienced problems while being flown by Russian flag carrier Aeroflot, which has been under heavy pressure from the government to add more Russian planes to its fleet.
In March, a plane had to cut short a scheduled flight after it encountered problems with its undercarriage.
Aeroflot's first Superjet plane also spent several weeks grounded upon delivery because of an air conditioning problem.
Sukhoi is a giant holding with a history going back to the 1930s in the Soviet Union. It employs 26,000 people and is based in the remote Far Eastern city of Komsomolsk-on-Amur and also makes military fighter jets.