A Russian-built airliner is feared to have crashed during a demonstration flight aimed at drumming up sales.
The jet, carrying 46 people, lost contact with air controllers while over mountains in western Indonesia.
Search and rescue teams are heading to the area but bad weather forced at least two helicopters to turn back.
The Sukhoi Superjet-100, a civilian plane, took off from Jakarta's Halim Perdanakusuma Airport at 2pm and was due to return 50 minutes later.
Controllers lost contact after it reportedly dropped from 10,000 feet to 6,000 feet near the Salak mountains in West Java.
Diplomats from the Russian Embassy, representatives from airline companies and journalists were among the passengers.
The plane, developed by the Russian aerospace company Sukhoi in co-operation with Western partners, is the first completely new airliner designed by Russia since the Soviet collapse.
It was on a "Welcome Asia!" road show with stops in countries stretching from Pakistan to Laos and Vietnam.
Russia has hoped that the short- to mid-range jet, which made its maiden run in 2008, will help it break into international markets dominated by Boeing and Airbus.