Several cars have been set on fire outside Birmingham prison after two masked men "armed with a firearm" were seen fleeing the scene.
West Midlands Police said the incident took place in a car park outside the compound with the two men "seen to make off in a vehicle".
No injuries were reported.
A West Midlands Fire Service spokesman added that two fire engines and 10 firefighters responded to the incident which involved "a number of cars".
The last firefighters left the scene shortly before 4pm.
Workers at a nearby scrapyard described hearing car alarms going off and coming out to see at least half a dozen cars already well alight.
They told how armed police arrived quickly at the scene, near the prison staff training building, along with other officers in both marked and unmarked cars.
Witness Warren Davies told the Birmingham Mail: “I saw a big ball of fire. It was coming from the three main cars.
“I heard the popping of the tyres and windows and all the police turned up.
He added that there was now a hole in the fence which appeared to have been made deliberately.
The paper reported that prison officers had seen two masked men spraying liquid onto cars, which were then lit damaging up to 10 vehicles.
Rob Kellett, director of the prison, said: "At approximately 13.30 this afternoon an incident took place in the car park across the road from HM Prison Birmingham.
"Nobody has been injured. West Midlands Police and the fire service are in attendance, and a fire has been extinguished."