West Midlands Police said the incident took place in a car park outside the compound.
The two men were “seen to make off in a vehicle”, police said.
No injuries were reported.
A West Midlands Fire Service spokesman added that two fire engines and 10 firefighters were responding to the incident which involved “a number of 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.