An Indonesian aircraft with 189 people on board crashed into the sea soon after taking off from the capital, officials say.
Lion Air flight JT610, an almost new Boeing 737 MAX 8, lost contact with ground officials 13 minutes after takeoff, and crashed about 15km off the coast.
Rescue officials said they had recovered some human remains from the crash site, about 15km off the coast.
An Indonesian search and rescue agency official estimated there would be no survivors from the crash.
"We need to find the main wreckage," Bambang Suryo, operational director of an Indonesian search and rescue agency, told reporters. "I predict there are no survivors, based on body parts found so far."
The Ministry of Foreign Affairs and Trade said there was no indication that any New Zealanders had been involved in the Lion Air plane crash.
A ministry spokesperson said the New Zealand Embassy in Jakarta was monitoring the situation closely and that there had no requests for consular assistance.
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."
Search and rescue crews have located the crash site.
Items such as handphones and life vests were found in waters about 30m to 35m 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," Mr Syaugi said. "We are trying to dive down to find the wreck."
Ambulances were lined up on the coast east of Jakarta and police were preparing rubber dinghies, a Reuters reporter said. Fishing boats were being used to help search.
The pilot had earlier asked to return to Jakarta's Soekarno-Hatta airport, the head of Pangkal Pinang's search and rescue office, Danang Priandoko, told local news outlet Kompas.
"It's correct that an RTB was requested and had been approved but we're still trying to figure out the reason," Soerjanto Tjahjono, head of Indonesia's transport safety committee, told reporters, referring to the pilot's request.
"We hope the black box is not far from the main wreckage so it can be found soon," he said, referring to the cockpit voice recorder and flight data recorder.
At least 23 government officials were on board the plane.
Beberapa serpihan pesawat Lion Air JT 610 yang jatuh di perairan Karawang. Pesawat membawa 178 penumpang dewasa, 1 penumpang anak-anak dan 2 bayi dengan 2 Pilot dan 5 FA. Basarnas dan Kementerian Perhubungan terus melakukan penanganan. Beberapa kapal tug boad berada di lokasi. pic.twitter.com/Gb6P4zjCQF— Sutopo Purwo Nugroho (@Sutopo_PN) October 29, 2018
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.
Plane maker Boeing said in a tweet that it was aware of reports of an airplane accident and it was "closely monitoring" the situation.
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, Mr Tjahjono said.
An MFAT spokesperson said the New Zealand Embassy in Jakarta is monitoring the situation closely and is in contact with local authorities to determine whether any New Zealanders are affected.
The Embassy has had no requests for consular assistance to date.
There are currently 321 New Zealanders registered as being in Indonesia.
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 US National Transportation Safety Board will automatically assist with the inquiry into the crash, backed up by technical advisers from Boeing and US-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.
Data from FlightRadar24 shows the first sign of something amiss was around two minutes into the flight, when the plane had reached 610m.
Then it descended more than 152m and veered to the left before climbing again to 1524m, where it stayed during most of the rest of the flight.
It began gaining speed in the final moments and reached 397mph before data was lost when it was at 1113m.
Its last recorded position was about 15km north of the Indonesian coast, according to a Google Maps reference of the last coordinates from Flightradar24.
Lion Air has previously been on an EU safety blacklist.
CNN reported that the International Air Transport Association had recently cleared the airline but it did not have the best safety record.
Established in 1999, it has had issues of safety and poor management in the past and was banned from flying into European airspace until 2016.
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 2013, Lion Air flight 904 crashed into the sea on landing at Bali's Ngurah Rai International Airport. All 108 people on board survived.
In 2011 and 2012 there was a spate of incidents where pilots were found in possession of methamphetamines, in one incident hours before a flight.
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 US planemaker's largest customers globally.
We're following reports that contact has been lost with Lion Air flight #JT610 shortly after takeoff from Jakarta.— Flightradar24 (@flightradar24) October 29, 2018
ADS-B data from the flight is available at https://t.co/zNM33cM0na pic.twitter.com/NIU7iuCcFu
- BBC / Reuters