Doomed Lion Air Flight 610 dropped at 'breakneck speed', according to new data, as officials confirmed the bodies of more passengers have been found in the sea off Jakarta.

The national deputy police chief Ari Dono Sukmanto confirmed the grim find, which included the remains of a baby.

Lion Air flight JT610 plunged into the sea off of Jakarta, the Indonesian capital, just minutes after it took off.

The troubled flight made erratic altitude changes in the brief time it was in the sky before it dramatically plunged and crashed into the sea.

Preliminary data transmitted by flight 610 now suggests the doomed plane dropped at breakneck speed — falling from an altitude of 1479m in just 21 seconds.

A normal descent for an airliner would be about 450m to 600m per minute, aviation safety expert John Cox told Bloomberg.

Data obtained by FlightRadar24 shows the Lion Air plane descending at more than 9400m per minute.

"This thing really comes unglued," said Cox, who runs consulting company Safety Operating Systems.

"The numbers are barely believable."

Six body parts had been filled with body parts already recovered. The recovery of bodies is being complicated because parts of the plane is submerged in water up to 30m deep.

Grieving relatives have provided dna samples to help try and identify their loved ones. The impact of the crash meant many victims bodies were not left intact.

Speculation is rising about what caused the aircraft carrying 189 people to crash.

Some reports suggest the aircraft had technical faults, while other experts say they're looking at the possibility of a bomb being involved.

But according to aviation consultant and former pilot Alastair Rosenschein, we won't have a definitive answer on what caused the crash until authorities recover the plane's black box.

"It is almost impossible to say just what happened," Rosenschein told CNN. "At this point, some sort of mechanical failure is probably the most likely, but this is purely speculative."

The aviation expert said that until the black box is found, it would remain unlikely authorities could figure out what brought down the plane.

He noted it's especially important to find the black box quickly because the doomed plane was a newer model.

"What happened here could possibly affect the same model of aircraft flying in other parts of the world," he said.

Investigators have deployed underwater beacons to trace the flight's black box recorders, but so far they are yet to make a discovery.

The top priority will be finding the cockpit voice recorder and flight data recorder to help determine the cause, safety experts said.

As the plane crashed in shallow water, recovering the black boxes should be easier than with deepwater crashes such as AirAsia Indonesia flight QZ8501 in 2014 and Air France flight 447 in 2009, said Greg Waldron, managing editor of Flightglobal Asia, an industry publication.

About three minutes after the Boeing 737 Max 8 took off for its one-hour flight to Pangkal Pinang, pilot Bhavye Suneja asked air traffic control for permission to turn around and return to Jakarta airport.

Ten minutes later, the plane crashed into waters off the Java coast.

An analysis of data from the crashed plane by the Aviation Safety website described its speed and altitude during its 13 minutes of flying as "erratic".

The plane made a climbing left-hand turn after takeoff, climbed to 640m and then dropped down to 450m.

It then climbed again and continued unsteadily for a few minutes between 1370m and 1630m before the fatal plunge.

The Boeing 737 Max involved in yesterday's crash had flown a different route on Sunday. Similar data shows it had erratic movements immediately after takeoff, but managed to climb and maintain a steady altitude.

Lion Air has confirmed the aircraft had a "technical problem" on the Sunday flight, "which had been resolved according to the procedure".

What caused the strange changes in altitude and speed, and why the pilot asked to return to Jakarta moments after takeoff, will now be a major focus for investigators.