A Lion Air passenger flight carrying 189 passengers crashed into the sea on Monday, shortly after taking off from the capital Jakarta.
The plane was heading to the city of Pangkal Pinang off the island of Sumatra when it lost contact with air traffic control around 6.30 am (2330 GMT), 13 minutes after takeoff.
"The plane had requested to return to base before finally disappearing from the radar," Sindu Rahayu, directorate general of Civil Aviation at the transport ministry, said.
Lion Air said the aircraft, which was a brand-new Boeing 737 MAX 8, was carrying 181 passengers, including one child and two babies, and eight crew members. There were two foreigners on board the plane: its pilot, originally from New Delhi, and an Italian citizen.
Sutopo Purwo Nugroho, a spokesman for the rescue agency, tweeted photos of debris including a crushed smartphone, books, bags and parts of the aircraft fuselage that had been gathered by search and rescue vessels.
Indonesian TV broadcast pictures of a fuel slick and debris field, while other debris thought to be from the plane, including aircraft seats, were reportedly found near an offshore refining facility.
Distraught friends and relatives prayed and hugged each other as they waited at Pangkal Pinang’s airport.
At the National Search and Rescue Agency headquarters in Jakarta, family members turned up, hoping desperately for news.
Feni, who uses a single name, said her soon to be married sister was on the flight, planning to meet relatives in Pangkal Pinang.
"We are here to find any information about my younger sister, her fiance, her in-law to be and a friend of them," said Feni.
"We don’t have any information," she told Associated Press. "No one provided us with any information that we need. We’re confused. We hope that our family is still alive."
Jakarta plane crash: Flight Lion Air JT610
Indonesia’s Finance Minister Sri Mulyani also arrived at the agency and met with its chief, seeking information about 20 finance ministry staff who were on the flight.
An official of Indonesia’s safety transport committee said the cause of the crash would not be known until the plane’s cockpit voice recorder and data flight recorder were recovered.
"We will collect all data from the control tower," Soerjanto Tjahjono said. "The plane is so modern, it transmits data from the plane and that we will review too. But the most important is the blackbox."
The Flightradar website tracked the plane, showing 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.
Preliminary flight tracking data from the website shows the aircraft climbed to around 5,000 feet (1,524 m) before losing, and then regaining, height, before finally falling towards the sea.
It was last recorded at 3,650 feet (1,113 m) and its speed had increased to 345 knots, the site showed.
The search and rescue agency said the flight ended in waters off West Java that are 30 to 35 meters (98 to 115 feet) deep.
The agency’s chief Muhammad Syaugi told a news conference that divers were trying to locate the wreckage.
We're following reports that contact has been lost with Lion Air flight #JT610 shortly after takeoff from Jakarta.
ADS-B data from the flight is available at https://t.co/zNM33cM0na pic.twitter.com/NIU7iuCcFu
— Flightradar24 (@flightradar24) October 29, 2018
Lion Air said the aircraft was airworthy and had only been in operation since August.
Its pilot and co-pilot had together amassed 11,000 hours of flying time, the airline said in a statement.
The accident is the first to be reported that involves the widely-sold Boeing 737 MAX, an updated, more fuel-efficient version of the manufacturer’s workhorse single-aisle jet.
The first Boeing 737 MAX jets were introduced into service in 2017.
Boeing was aware of the reports and was "closely monitoring" the situation, its spokesman told Reuters.
Indonesia relies heavily on air transport to connect its thousands of islands but has a poor aviation safety record and has suffered several fatal crashes in recent years.
A 12-year-old boy was the sole survivor of a plane crash that killed eight people in mountainous eastern Indonesia in August.
In August 2015, a commercial passenger aircraft operated by Indonesian carrier Trigana crashed in Papua due to bad weather, killing all 54 people on board.