Firefighters battled a fire at a used truck dealership in Plaistow on Tuesday that forced police to shut down a section of Route 125.Fire crews were called to Diesel World on Plaistow Road about 4 p.m. Employees were evacuated, and there were no reports of injuries.Fire Chief John McArdle said a truck was burning inside the building."On our arrival, I saw smoke and fire coming out of the overhead, and the employees told me that there was a boom, which was followed by a lot of crackling, which indicates there was a fire in the overhead," he said.Investigators said the cause of the fire hasn't been determined."There was a truck in the showroom, that's obviously gone," McArdle said. "They also had some materials and products in the basement."The road reopened around 8:30 p.m. Tuesday.