An Indonesian aircraft with 189 people on board crashed into the sea and sank on Monday soon after taking off from the capital, Jakarta, on a flight to a tin-mining region, officials said.
Lion Air flight JT610, an almost new Boeing 737 MAX 8, lost contact with ground officials 13 minutes after takeoff, and crashed about 15 km (9 miles) off the coast.
Indonesia is one of the world's fastest-growing aviation markets, although its safety record is patchy. If all aboard have died, the crash would be the country's second-worst air disaster since 1997, industry experts said.
"We don't know yet whether there are any survivors," search and rescue agency head Muhmmad Syaugi told a news conference, adding that no distress signal had been received from the aircraft's emergency transmitter.
"We hope, we pray, but we cannot confirm."
Items such as handphones and life vests were found in waters about 30 metres to 35 metres (98 to 115 ft) deep near where the plane, a Boeing 737 MAX 8, lost contact, he said.
"We are there already, our vessels, our helicopter is hovering above the waters, to assist," Syaugi said. "We are trying to dive down to find the wreck."
Ambulances were lined up at Karawang, on the coast east of Jakarta and police were preparing rubber dinghies, a Reuters reporter said. Fishing boats were being used to help search.
At least 23 government officials were on board the plane, which an air navigation spokesman said had sought to turn back just before losing contact.
Edward Sirait, chief executive of Lion Air Group, told reporters the aircraft had a technical problem on a flight from the resort island of Bali to Jakarta but it had been "resolved according to procedure".
Sirait declined to specify the nature of the issue but said none of its other aircraft of that model had the same problem. Lion had operated 11 Boeing 737 Max 8s and it had no plan to ground the rest of them, he said.
The accident is the first to be reported involving the widely sold Boeing 737 MAX, an updated, more fuel-efficient version of the manufacturer's workhorse single-aisle jet.
Privately owned Lion Air said the aircraft had been in operation since August, was airworthy, with its pilot and co-pilot together having accumulated 11,000 hours of flying time.
The head of Indonesia's transport safety committee said he could not confirm the cause of the crash, which would have to wait until the recovery of the plane's black boxes, as the cockpit voice recorder and data flight recorder are known.
"The plane is so modern, it transmits data from the plane, and that we will review too. But the most important is the blackbox," said Soerjanto Tjahjono.
Safety experts say nearly all accidents are caused by a combination of factors and only rarely have a single identifiable cause.
The weather was clear, Tjahjono said.
President Joko Widodo told a news conference authorities were focusing on the search and rescue, and he called for the country's prayers and support.
The effort to find the wreckage and retrieve the black boxes represents a major challenge for investigators in Indonesia, where an AirAsia Airbus jet crashed in the Java Sea in December 2015.
Under international rules, the U.S. National Transportation Safety Board will automatically assist with the inquiry into Monday's crash, backed up by technical advisers from Boeing and U.S.-French engine maker CFM International, co-owned by General Electric and Safran.
Boeing was deeply saddened by the loss, it said in a statement, and was ready to provide technical assistance for the investigation.
The flight took off from Jakarta around 6.20 a.m. and was due to have landed in Pangkal Pinang, capital of the Bangka-Belitung tin mining region, at 7.20 a.m., the Flightradar 24 website showed.
Data from FlightRadar24 shows the first sign of something amiss was around two minutes into the flight, when the plane had reached 2,000 feet (610 m).
Then it descended more than 500 feet (152 m) and veered to the left before climbing again to 5,000 feet (1,524 m), where it stayed during most of the rest of the flight.
It began gaining speed in the final moments and reached 345 knots (397 mph) before data was lost when it was at 3,650 feet (1,113 m).
Its last recorded position was about 15 km (9 miles) north of the Indonesian coast, according to a Google Maps reference of the last coordinates from Flightradar24.
Indonesia's worst air disaster was in 1997, when a Garuda Indonesia A300 crashed in the city of Medan killing 214 people.
Founded in 1999, Lion Air's only fatal accident was in 2004, when an MD-82 crashed upon landing at Solo City, killing 25 of the 163 on board, the Flight Safety Foundation's Aviation Safety Network says.
In April, the airline announced a firm order to buy 50 Boeing 737 MAX 10 narrowbody jets with a list price of $6.24 billion. It is one of the U.S. planemaker's largest customers globally.