The fire was reported around 10:30 a.m. at 1401 King Road in West Whiteland, Pa. at a company called Johnson Matthey.
An evacuation has been ordered for 1300 feet around the fire.
The Red Cross says they will be on location at the East Whiteland Fire department to assist with a reception center for residents that have been evacuated.
Patty Mains, a spokeswoman for Chester County Department of Emergency Services, says the trailer is still on fire at the Johnson Matthey plant. She says the plant itself was evacuated, as well as some houses in the area.
The view from Chopper 6 HD showed a number of people standing outside the building while firefighters worked to douse the flames.
One person was injured. The victim was taken to Crozer Chester Medical Center in an unknown condition.
King Road is shut down between Ravine and Phoenixville Pike.
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