The jet vanished from radar just 13 minutes after taking off from the Indonesian capital, plunging into the ocean.
Video footage apparently filmed at the scene of the crash showed a slick of fuel on the surface of the water.
Disaster agency spokesman, Sutopo Nugroho, tweeted pictures of debris, including what appeared to be an emergency slide and various parts of a smashed mobile phone.
Search and Rescue Agency spokesman Yusuf Latif said authorities were still searching for the remains of the plane, which lost contact with air traffic control around 6.30 am (2330 GMT), en route to Pangkal Pinang on the island of Bangka.
“The plane crashed into the water about 30 to 40 metres deep,” he told AFP.
Sindu Rahayu, directorate general of Civil Aviation at the transport ministry, said the aircraft was carrying 178 adult passengers, one child and two babies, with two pilots and five flight attendants.
“The plane had requested to return to base before finally disappearing from the radar,” he added in a statement.
The Flightradar website tracked the plane — which it said was a Boeing 737 — and showed it looping south on take-off and then heading north before the flight path ended abruptly over the Java Sea, not far from the coast.