Relatives of passengers of Lion Air flight JT610 that crashed into the sea, cry at Depati Amir airport in Pangkal Pinang, Indonesia, October 29, 2018. (Photo: Antara/Elza Elvia via Reuters).

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 Lion Air 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, an official of state energy firm Pertamina said.

Wreckage had been found near where the Lion Air 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. "We hope, we pray, but we cannot confirm."

Flight JT610 took off 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.

Lion Air's Malaysian subsidiary, Malindo Air, received the very first global delivery.

Boeing is aware of the airplane accident reports and is "closely monitoring" the situation, it said on social network Twitter.