Police received a report of a man pointing a gun at another motorist on the M5 before a driver was shot dead by officers just off the motorway near Bristol, the West Mercia force said on Thursday.
A man was reportedly shot up to 10 times by armed police after officers swooped on a car on a busy A-road in near Portishead, North Somerset, and shot him through the passengers window on Wednesday.
West Mercia Police said they were contacted at about 8.30am about the incident involving an alleged gunman near junction eight of the motorway.
The victim was shot about an hour later.
A West Mercia Police spokesman said: “We can confirm that we received a call at 8.30am yesterday of a report of a man in a vehicle, pointing a gun at another motorist and that was near junction eight of the M5.
“That was passed on to the central motorway police group. We have informed the Independent Police Complaints Commission about this call.”
The force said that people travelling on the M5 had contacted police after seeing a man in a car with a handgun.
The vehicle left the motorway at junction 19 and officers stopped it on the A369, known as the Portbury Hundred.
The Independent Police Complaints Commission is investigating.
A post-mortem examination was due to take place on Thursday.