EAST HUNTINGDON, Pa. (KDKA) – A trailer caused an explosion and fire in Westmoreland County, prompting an evacuation of the surrounding area.

WATCH: KDKA’s Pam Surano Reports Live From East Huntingdon Township

The Westmoreland County supervisor reported that a truck containing propane exploded and was on fire in the 1500 block of New Stanton Ruffsdale Road at a Sterling Transport facility. The fire was reported shortly before 4:30 p.m.

Three employees were hurt. Two of the victims were taken by helicopter to UPMC Mercy’s burn unit and the third was transported by ground.

One person is in critical condition, one is seriously hurt and a female worker is in moderate condition.

Two workers were inside the building at the time, and two were outside the facility.

One of the employees hurt is a truck driver.

“We had a large explosion inside the building,” E. Huntingdon Township Assistant Fire Chief James King said. “They were changing a butane trailer. They were doing a repair on the valve. That is what let loose. It depressurized for about 15 minutes until it bled off.”

WATCH LIVE: News Chopper 2 flies over the scene —

Crews could be seen trying to put out a fire at a building in East Huntingdon Township. A HAZMAT Team was also called in.

(Photo Credit: KDKA)

New Stanton Ruffsdale Road at Thompson Hollow Road was closed. A long line of lights from first responders’ vehicles stretched down the road.

Large flames could be seen shooting out of the roof along with thick plumes of dark smoke. The tanker was inside a garage at Fleet Services when it exploded, catching the building on fire.

(Photo Credit: NewsChopper 2)

The tankers reportedly have propane inside.

(Photo Credit: KDKA Viewer Pete)

When NewsChopper 2 was flying to the scene, the smoke could be seen from over 40 miles away.

KDKA’s Pam Surano reports hours later, crews are still on scene, tearing down the garage.

Stay with KDKA for the latest on this developing story.