Body parts, twisted wreckage and clothing were plucked from waters off the Indonesian capital on Sunday after a passenger jet with 62 people aboard crashed shortly after take-off a day earlier.

Authorities have yet to say why the Sriwijaya Air Boeing 737-500 went into a steep dive about four minutes after it left Soekarno-Hatta international airport on Saturday afternoon.

But, on Sunday, they said that they had pinpointed the location of its black boxes — cockpit voice and flight data recorders — that could be key to explaining why the plane slammed into the Java Sea off the sprawling city's coast.

The search and rescue agency said it had collected body bags filled with human remains, as well as debris from the wreckage, in waters about 23 metres deep.

Passengers Ihsan Adhlan Hakim and his new bride Putri were headed to Pontianak, the city on Indonesia's section of Borneo Island which had been flight SJ182's destination, about 90 minutes away.

"He called me to say that the flight was delayed due to bad weather," Hakim's brother Arwin said from Pontianak, where a wedding celebration had been planned for the newlyweds.

"That was the last time I had contact with him."

Steep dive 

Beben Sofian, 59, and her husband Dan Razanah, 58 were also on the doomed flight.

"They took a selfie and sent it to their kids before taking off," the couple's nephew, Hendra, told AFP.

DNA from relatives will be compared with discovered remains for identification.

All 62 passengers and crew aboard the half-full flight was Indonesian. The count included 10 children.

Distraught relatives waited nervously for news at Pontianak airport.

"I have four family members on the flight — my wife and three children," said a sobbing Yaman Zai.

"[My wife] sent me a picture of the baby... How could my heart not be torn into pieces?"

Data from FlightRadar24 indicated that the airliner reached an altitude of nearly 3,350 metres before dropping suddenly. It then lost contact with air traffic control.

The transport minister said on Saturday that the jet appeared to deviate from its intended course just before it disappeared from radar.

"The aircraft's final moments are... very concerning as the speed that [it] was flying at that altitude was much lower than expected," said Stephen Wright, professor of aircraft systems at Finland's Tampere University.

"The last seconds saw the aircraft rapidly descend from 3,000 km to the sea in a matter of 20 seconds, which implies a catastrophic event or something deliberate."

But he added that the crash can "only be fully explained once the black boxes and wreckage can be properly analysed".

Sriwijaya Air, which operates flights to destinations in Indonesia and southeast Asia, has said little so far about the 26-year-old plane, which was previously flown by US-based Continental Airlines and United Airlines.

The Indonesian carrier has not recorded a fatal crash since it started operations in 2003, but this accident is the latest in a string of disasters for the country's aviation sector.

The southeast Asia nation's aviation sector has long been marred by safety concerns, and its airlines were once banned from entering US and European airspace.

Safety concerns 

In October 2018, 189 people were killed when a Lion Air Boeing 737 MAX jet crashed near Jakarta.

That accident — and another in Ethiopia — saw Boeing hit with $2.5 billion in fines over claims it defrauded regulators overseeing the 737 MAX model, which was grounded worldwide following the accidents.

The 737 that went down on Saturday was not a MAX variant.

"Our thoughts are with the crew, passengers, and their families," Boeing said in a statement.

In 2014, an AirAsia plane headed from Surabaya to Singapore crashed with the loss of 162 lives.

A final report said major factors included a chronically faulty component in a rudder control system, poor maintenance, and the pilots' inadequate response.

A year later more than 140 people, including scores on the ground, were killed when a military plane crashed shortly after take-off in Medan on Sumatra island.