An Indonesian Sriwijaya Air plane is feared to have crashed into the sea after the Boeing 737 lost contact with air traffic control in the capital Jakarta, with flight tracking data showing the jet plunged into a steep dive just four minutes after take-off.

It was unclear how many passengers and crew were aboard the Boeing 737-500, which has a capacity of about 130, when it left Jakarta's Soekarno-Hatta international airport Saturday afternoon.

The usual flight time is about 90 minutes over the Java Sea between Java island and Kalimantan, Indonesia's section of Borneo island.

Data from FlightRadar24 said the plane reached an altitude of nearly 11,000 feet (3,350 metres) before dropping to 250 feet. It then lost contact with air traffic control.

"Sriwijaya Air flight #SJ182 lost more than 10,000 feet of altitude in less than one minute, about 4 minutes after departure from Jakarta," the tracking agency said on its official Twitter account.

Broadcaster Kompas TV quoted local fishermen as saying they had found debris near islands off the coast of Jakarta, but it could not be immediately confirmed as having belonged to the missing jet.

Indonesia's transport ministry said it was probing the incident.

"A Sriwijaya (Air) plane from Jakarta to Pontianak (on Borneo island) with call sign SJY182 has lost contact," said ministry spokesman Adita Irawati.

"It last made contact at 2:40 pm (0740 GMT)."

The budget airline, which has about 19 Boeing jets that fly to destinations in Indonesia and Southeast Asia, said only it was investigating the loss of contact.

Indonesia's search and rescue agency and the National Transportation Safety Commission were also investigating, Irawati said.

In October 2018, 189 people were killed when a Lion Air Boeing 737 MAX jet slammed into the Java Sea about 12 minutes after take-off from Jakarta on a routine one-hour flight.

That crash -- and a subsequent fatal flight in Ethiopia -- saw Boeing hit with $2.5 billion in fines over claims it defrauded regulators overseeing the 737 MAX model, which was grounded worldwide following the two deadly crashes.

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