People have reported hearing a "very loud" noise, akin to an explosion, which is believed to have come from a military aircraft. It happened at around midday on Saturday.
The noise was reported in Leicestershire, with people reporting it across a wide area. A spokesperson for Leicestershire Fire and Rescue Service said the boom had been heard at its control centre in Leicester as well as at fire stations in Market Harborough and Melton. That would suggest it was caused by a plane, reports LeicestershireLive.
The sound was also reported across Northamptonshire and by people in Banbury and Oxford. Leicestershire Police said it had received "numerous calls" but there was no need for concern.
On social media, plane spotters suggested the sound may have come from an RAF Typhoon fighter jet scrambling to intercept another aircraft in distress. The RAF's Airbus Voyager, the air force's only in-flight refuelling plane, was being tracked by at least 1,440 people on Flightradar24 - a site that tracks aircraft in real time.
A statement published by 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."
One person said on Twitter: "According to my plane spotter son, the sonic boom was caused by a fighter jet scrambling to assist a plane that had squawked an emergency."
When contacted by LeicestershireLive, a spokeswoman for fire control said: "I know what you're going to ask! We felt it here at Meridian.
"We thought it was a large lorry going past at first. It was also felt in Melton and at Market Harborough, so that wouldn't suggest it was anything happening on the ground to be concerned about."
She said that a plane breaking the sound barrier was the most likely cause. People around Leicestershire have been tweeting about the boom, with one saying: "Sonic boom??? Was really loud."
Another said: "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?"
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One said: "Heard and felt a big explosion in #Leicester just now. Saw some suggesting a sonic boom?" Others heard the sound in Northamptonshire.
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.
As long as the aircraft is flying at Mach 1 it will generate continuous sound waves, known as a boom carpet. An aircraft flying at 20,000 feet would create a sonic boom cone 20 miles wide.
