People across Leeds were baffled by a mysterious 'loud bang' or 'explosion' heard across the city last night.
Confused locals complained about the noise on social media, with some saying the noise could be heard as far away as Leeds Bradford Airport.
Some claimed the sound was so loud it shook the bricks of their homes.
West Yorkshire Police have since said that the sound heard in the Leeds and Doncaster areas was believed to have been caused by a sonic boom from an aircraft.
"Nothing to worry about," the force tweeted last night.
The first reports were posted on a Leeds online community group sometime around 9pm, with most who heard it around the south east of the city, reports Leeds Live.
There were reports of the noise from Saxon Gardens in the west to around Whinmoor to the east.
Some residents in LS9 said the noise was so loud it shook their property.
One resident described the sound as like "something exploding".
Another claimed to have heard an engine around the same time, and suggested the noise was a "sonic boom" of some kind.
There were also unconfirmed reports of a similar 'sonic boom' sound in parts of Salford, in Greater Manchester, around the same time.
