Flight JT 610 was on a scheduled flight to Pangkal Pinang, the main town in the Bangka Belitung Islands.
It lost contact with ground control a few minutes after take-off, and was last tracked crossing the sea - it is unclear if there are any survivors.
The plane was a Boeing 737 MAX 8, a brand new type of aircraft.
Flight JT 610 took off from Jakarta at 06:20 local time on Monday morning (23:30 GMT on Sunday).
