Relatives russia plane crash java
Anxious relatives await news after the Russian Superjet crashed in Java

Rescue workers in western Indonesia have found the wreckage of the Russian aircraft which went missing on Wednesday during a demonstration flight.

The fate of the 48 passengers on board is not known. The rescue team has not been able to reach the exact spot and the precise number of people on board is still not certain.

"The airplane crashed at the edge of Salak Mountain ... An investigation must be done immediately and thoroughly," Reuters quoted President Susilo Bambang Yudhoyono as telling a televised news conference.

The search was halted in between due to bad weather and later a search helicopter spotted the wreckage along a mountain in the region, the Associated Press quoted Maj Ali Umri Lubis as telling Metro TV.

"The helicopter just informed us that they spotted the wreckage about 10 minutes ago. It was at about 5,000 feet. The condition of the wreckage is still unclear," Lubis said.

The Sukhoi superjet 100 disappeared from radar 21 minutes after takeoff while it was flying over West Java in Indonesia. The aircraft took off from the Halim Perdanakusuma Airport in Jakarta.

The brand new aircraft reportedly carried potential buyers and journalists for the second demonstration of the day.

"The first demonstration flight in the morning went smoothly. There were no problems," CNN quoted Sunaryo an official with Sukhoi's Indonesian agent as saying.

This is Russia's first new passenger jet since the fall of the Soviet Union and was being seen as the nation's chance for re-entry into the international aircraft market.

A spokesperson for Russia's United told Reuters that the plane was part of a demonstration programme in Indonesia called Asian Roadshow, aimed at promoting the aircraft. It was due to fly on to Laos and Vietnam.

"The first flight was carried out in a normal mode. The pre-flight preparations were carried out in full and the place was ready to fly.

According to information from Indonesia, the contact with the plane was broken after 20 minutes from takeoff, at 1435 local time. Search works are under way," the spokesperson added.

A major accident, if confirmed, would shatter Russia's image and plunge it back to the Soviet-era days of frequent air crashes and faulty aircraft.

The Superjet project was a joint venture between the legendary Sukhoi and Italy's Alenia Aeronautica, which is part of the aerospace and defence giant Finmeccanica.