Investigators state that the Sukhoi Superjet 100 missing in Indonesia had been on its second demonstration flight of the day when it disappeared.
The aircraft lost radar contact near the town of Bogor, Java, says Indonesian director general for civil aviation Herry Bakti.
He says it took off from Halim airport, Jakarta, and was fuelled for a 4h flight but has been missing for 3h.
Contact was lost near a mountain, Mount Salak, which rises to over 7,000ft, Bakti says.
He adds that there were 44 occupants including airline officials and journalists. The jet was on its second flight of the day, having flown a demonstration for government personnel earlier.
"It is missing and we have lost contact," Bakti says.
It is unclear which airframe is missing. Sukhoi had been intending to fly its prototype 95005 on an Asian tour, but photographs appear to identify the twinjet involved as a separate prototype, 95004. The Indonesian authority has not confirmed the aircraft's identity.
Sukhoi says the first demonstration flight "took place normally", and that the aircraft was technically "fully functional".
Communications were lost 20min into the flight, which departed at 14:35 local time. "We are carrying out search operations [and have] set up operational headquarters," adds the company.