Dozens of people in and around Leicester have reported hearing an explosion or a sonic boom overhead.
The sound was also reported across Northamptonshire and by people in Banbury and Oxford.
The loud bang led to a swift reaction on social media as people speculated about the cause, including whether it was a jet breaking the sound barrier.
Twitter user Dr Jon Sutton said: “Massive boom heard over a wide area of Leicestershire. Aircraft, or meteor?”
Naomi tweeted: “Anyone in Leicester know what the hell that massive explosion was?? It shook our house and the birds are going crazy.”
Another user wrote: “Very loud boom in Leicester about 15 mins ago. Felt the air shake – cats scared and ran indoors. Very unnerving – what the hell was it?”
Reports later emerged it may have been an RAF Typhoon aircraft scrambled from RAF Coningsby in Lincolnshire to intercept a Dash 8 plane that had experienced radio failure, which later landed at an airfield in Epping.
Leicestershire police said: “We have received numerous calls in relation to a large explosion sound heard from various parts of the city and county.
“We like to reassure you that there is no concern however thank you for your immediate response to us.”
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The neighbouring Northamptonshire force said: “Police and fire services in Northamptonshire have received numerous calls in relation to a large explosion sound heard from various parts of the county.
“We would like to reassure people there is no concern, but thank you for contacting us.”
A sonic boom is caused when planes fly faster than the speed of sound, which at ground level is around 761mph.
When travelling at this speed, also known as Mach 1, the aircraft displaces the air and creates pressure waves that become compressed and then released in a shock wave.