STAFF at a computer firm at Middlebrook Retail Park were evacuated for more than two hours after a gas leak.
The fire service cordoned off Scan Computers International, on the Enterprise Park at Middlebrook, after their gas main was ruptured.
It is believed that the damage was done by a vehicle, as brickwork surrounding the exterior pipe was also damaged.
Crews from Horwich and Bolton Central were called to the retail park just before 9am, while police also attended to close a nearby road.
Firefighters ventilated Scan's premises and the gas company was able to isolate the leak promptly, allowing the computer firm and neighbouring businesses to reopen.
Scan's staff are on the verge of being allowed back into the building and are waiting for final approval from the gas company.
A fire service spokesman said: "It looks as though it was hit by an unknown vehicle, which was not found.
"We put a cordon of 50 metres in place around the building and requested the assistance of the gas company."