Four men who were being followed by an unmarked police car have been killed in a road collision in Bradford, police say.
The Independent Office for Police Conduct (IOPC) is investigating the crash which involved a BMW on Bingley Road in the early hours of Thursday.
Witnesses are reported to have described a loud bang and a large amount of police activity with a number of cars involved in the crash.
"It is understood at this time that the car was being followed by an unmarked police car at the time of the crash,” an IOPC spokeswoman said.
One resident on the road told the Bradford Telegraph and Argus that the street was "like a race track at night."
She added: "I heard a loud bang and went outside and there was lots of police."
A woman who lives on a nearby side-street told the newspaper that she was woken up by the loud noise and rushed to see what had happened.
"When I got there I saw a BMW which had crashed. The police were already there and one of the officers told me to go back inside but I stayed there because I was concerned."
IOPC regional director Miranda Biddle said: "This is a most tragic incident and our sympathies are with the family and friends of those who have died.
"West Yorkshire Police made a mandatory referral to the IOPC and at 6.24am we declared an independent investigation. Our investigators are attending post-incident procedures, have travelled to the scene and have begun gathering evidence."
Police confirmed that four men died in the collision at the junction in Toller Lane in Bradford, and that the road is currently closed and likely to remain so for most of today.
