A huge "explosion" heard across Shrewsbury, Shropshire, is thought to have been an RAF Eurofighter Typhoon aircraft breaking the sound barrier.
Trails were left by two planes, said witness Andy Brooks
The boom was heard at about 1610 GMT. Spokesman for RAF Shawbury, Martin Locke said he did not know what the plane was doing over Shropshire.
One of the many callers to BBC Radio Shropshire, Jackie Cassidy said: "It was really frightening."
She said she heard a bang, the windows shook and the door came ajar.
Mrs Cassidy, who works for Hatchers solicitors in Shrewsbury said: "I thought it was an earthquake or a gas explosion."
Nobody knew what was going on, she said, and everyone poured out on to the streets.
Witness Andy Brooks said: "After the boom, the clouds just parted and this (smoke trail) is what I saw."
Another caller to BBC Radio Shropshire said he saw two large aircraft flying very low near Haughmond Hill.
The station also received calls from the town centre, Shelton and Belle Vue areas.
News editor Sharon Simcock said: "We thought someone had driven into our building."