"The RAF (Royal Air Force) can confirm Quick Reaction Alert Typhoon aircraft were launched this morning... to intercept a civilian aircraft," Britain's defence ministry said in a statement.

"The aircraft was safely escorted to Stansted Airport."

The plane, en route from the Indian city of Mumbai to Newark in the United States, made a "precautionary landing" at the airport following a "bomb threat", Air India said in a tweet that was subsequently deleted.

British police said the plane was diverted to Stansted at around 9:50am local time (0850 GMT) following "reports of a security alert".

"The plane is currently at the airport and officers are making enquiries," Essex police said on Twitter.

Stansted Airport, northeast of London, said the Boeing 777 landed there 25 minutes later with police in attendance.

"It is parked on an isolated stand away from the normal airport operations," it added in a statement, noting its runway had fully reopened.

British reports suggested the scrambled fighter jets had caused a sonic boom heard across the impacted area.

"The Typhoon aircraft were authorised to transit at supersonic speed for operational reasons," the defence ministry said.

"Any inconvenience caused to local residents is regretted."