Armed police have offered the first explanation for a dramatic operation in which they shot dead a man inside his car on the M5 motorway, in south-west Britain.

Officers from Avon and Somerset police opened fire on a red Suzuki Swift at 9:30 a.m. on Wednesday morning not far from the city of Bristol, and he was declared dead shortly afterwards.

In a statement, the police force said it acted because “we received calls from concerned members of the public travelling on the M5 who reported they had seen a man in a car with a handgun.”

Witnesses described officers firing between six and 10 shots into the car, which came to a stop on the A369 road by the town of Portishead, Somerset, which links traffic to the M5.

Dave Ellison told BBC Radio Bristol: "They surrounded it. They shot maybe five, six or ten times. Then they dragged a man from the car to resuscitate him. It came off the roundabout towards Portishead and then was boxed in by cars."

Images broadcast by Sky News, and annotated by Business Insider, show six bullet holes in the car, which had a black handgun on its roof.

Portishead car bullet holes Sky News

Foto: The suspect's Suzuki Swift. source Sky News/Business Insider

More detail on the shooting was offered by the Independent Police Complaints Commission, which investigates all police activity that ends in death or serious injury.

A statement issued on Wednesday night said: "We have been advised that officers were responding to reports of a man travelling on the M5 with a handgun and that he had threatened another motorist."

The IPCC will take testimony from officers involved and examine other evidence, including CCTV footage.

The statement added: "What appears to be a non-police issue firearm was found at the scene and will also be subject to examination."

The man who was killed has not yet been named. His body was covered with a white cloth shortly after he was taken out of the car. His body is due to undergo a post-mortem examination on Thursday.