A sonic boom was heard across Derbyshire as military aircraft were launched to intercept a passenger plane following a reported bomb threat.
Police and the fire service received “a large number” of 999 calls from people who feared there had been an explosion. Some residents said their homes shook.
Emergency services initially could not explain the cause of the loud bang heard shortly before 10:00 BST.
The RAF confirmed a Typhoon aircraft had been launched.
“The RAF can confirm Quick Reaction Alert Typhoon aircraft were launched this morning from RAF Coningsby to intercept a civilian aircraft,” a statement said.
“The aircraft was safely escorted to Stansted airport. The Typhoon aircraft were authorised to transit at supersonic speed for operational reasons; any inconvenience caused to local residents is regretted.”
Bob Billington, who lives in Derby, said he heard two bangs in quick succession and guessed it was a sonic boom.
“The first bang was rather loud, like the thunder from a very close lightning strike, then rather less than a second later there was a second, not quite as loud, and then the echoes from the surrounding buildings making it sound like a fairly short roll of thunder,” he said.
Mr Billington recognised the sound from hearing it at air shows “in the good old days”.
“They aren’t allowed to do that any more,” he said.
“I assume there aren’t very many of the people reporting it have actually heard one before, so I can understand their reactions.”
Derbyshire Police said they had received “a large number” of 999 calls about the noise.