"We are certain that the plane crashed into the sea and is submerged at a depth of 30 to 35 meters", National Search and Rescue Agency (Basarnas) head M. Syaugi told a press conference on Monday.
The flight, which departed at 6.20am this morning (29th October), was expected to land in Pangkal Pinang at 7.20am but lost contact with air traffic controllers at 6.33am.
At least 189 people are believed to have been on board the Indonesian budget carrier's passenger plane when it crashed into the ocean.
The Max 8 is part of Boeing Co.'s latest narrow-body 737 series.
The pilot and co-pilot had more than 11,000 hours of flying time between them, it added. That ban was lifted in June, as the US lifted a decade-long ban in 2016.
A passenger feared dead in the Indonesian plane disaster sent a selfie to his wife just before take-off, it has emerged.
In 2013 a Lion Air jet with a rookie pilot at the controls undershot the runway and crashed into the sea in Bali, splitting the plane in two.
"We are still confirming data on the names against the flight manifest", Nufransa said on Monday.
Novie Riyanto, the head of AirNav, which manages air traffic in Indonesia, said the pilot made a "RTB" or return to base request "just two or three minutes after it took off and the ATC has approved".
Family members arrive a Jakarta airport after Lion Air crash.
"Lion Air is very concerned about this incident and will work with relevant agencies and all parties", said spokesman Danang Mandala Prihantoro.
Indonesia's rescue agency says they have found plane debris at the crash site, while a statement from Boeing on its Twitter handle said that "Boeing is aware of reports of an airplane accident and is closely monitoring the situation".
Following the crash, Australia's Smart Traveller website advised that Australian government officials and contractors have been instructed not to fly on Lion Air. 'We are also confused about the why, since it was a new plane'.
Lion Air, a low-priced carrier, has a spotty safety record, with a number of incidents over the years, including a crash landing at sea in April 2013 that remarkably resulted in no deaths or serious injuries.
"The South African embassy in Jakarta has obtained a passenger manifest for the said flight and, based on this passenger manifest, indications are that there were no South African nationals on board the Lion Air flight JT 610", he said.