The West Midlands police said Tuesday that there had been no casualties from the incident which involved two masked men spraying an unknown substance on cars before setting them on fire.
The men were armed and threatened prison officers who had walked onto the car park to stay back. The men then set the cars on fire and escaped over the fence, Presstv reported.
“Several cars have been set on fire. There are no reported injuries. Two masked men, reportedly armed with a firearm, were seen to make off in a vehicle,” said a police statement.
There was no indication the arson attack could have terrorist motives.
Prison authorities said no one had been injured in the incident which took place at 13.30 p.m. local time.
"Nobody has been injured. West Midlands Police and the fire service are in attendance, and a fire has been extinguished,” said Rob Kellett, director of HM Prison Birmingham.