• Aircraft believed to have sunk, wreckage found
• Plane lost contact within minutes off takeoff from Jakarta
• Rescue agency officials don't know whether there are survivors
• No signal received from emergency locator, official says

JAKARTA: An aircraft with 189 people on board is believed to have sunk after crashing into the sea off Indonesia's island of Java on Monday, shortly after takeoff from the capital on its way to the country's tin-mining hub, officials said.

A spokesman for Indonesia's search and rescue agency said the Lion Air flight, JT610, lost contact 13 minutes after takeoff, adding that a tug boat leaving the capital's port had seen the craft falling.

"It has been confirmed that it has crashed," the spokesman, Yusuf Latif, said by text message, when asked about the fate of the plane, which air tracking service Flightradar 24 identified as a Boeing 737 MAX 8.

Debris thought to be from the plane, including aircraft seats, was found near an offshore refining facility in the Java Sea, an official of state energy firm Pertamina said.

Wreckage had been found near where the plane lost contact with air traffic officials on the ground, said Muhmmad Syaugi, the head of the search and rescue agency.

"We don't know yet whether there are any survivors," Syaugi told a news conference, adding that no distress signal had been received from the aircraft's emergency locator transmitter.

"We hope, we pray, but we cannot confirm."

An official of Indonesia's safety transport 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.

"We will collect all data from the control tower," said Soerjanto Tjahjono. "The plane is so modern, it transmits data from the plane and that we will review too. But the most important is the blackbox."

Australia had not received signals from the plane's emergency locator either, it told Indonesia in a reply to a query, agency chief Syaugi said.

The effort to locate the wreckage and retrieve the black bloxes will represent the second major deep sea recovery challenge for Indonesian investigators after an AirAsia Airbus jet crashed into the Java Sea in December 2015.

Under international rules, the US National Transporation 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 is aware of the airplane accident reports and is "closely monitoring" the situation, a company spokesman told Reuters.

The flight took off from Jakarta around 6.20 a.m. and was due to have landed in the capital of the Bangka-Belitung tin mining region at 7.20 a.m., the Flightradar 24 website showed.

"We cannot give any comment at this moment," Edward Sirait, chief executive of Lion Air Group, told Reuters, adding that a news conference was planned for later on Monday. "We are trying to collect all the information and data."

Preliminary flight tracking data from Flightradar24 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 risen to 345 knots, according to raw data captured by the respected tracking website, which could not immediately be confirmed.

Its last recorded position was about 15 km (9 miles) north of the Indonesian coastline, according to a Google Maps reference of the last coordinates reported by Flightradar24.

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.

The very first global delivery went to Lion Air's Malaysian subsidiary, Malindo Air.

Indonesia is one of the world's fastest-growing aviation markets, but its safety record is patchy.

Founded in 1999, Lion Air's only fatal accident to date was in 2004, when an MD-82 crashed upon landing at Solo City, killing 25 of the 163 people on board, the Flight Safety Foundation's Aviation Safety Network says.

However, six other Lion Air jets, including one that crash-landed in the water short of the runway at the Indonesian resort island of Bali in 2013, were damaged beyond repair in various accidents, according to Aviation Safety Network.

Lion Air was removed from the European Union's air safety blacklist in June 2016.

The privately owned airline in April 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.