Several nearby homes have been evacuated, and officials are considering evacuating more, including a an elderly couple that would need to be moved by emergency personnel.
Officials say the train carried the truck about 100 yards down the tracks. It wasn't immediately clear how the crash occurred, WPXI reported.
Don Lloyd, a truck driver experienced with carrying hazardous materials who was working nearby, rushed to the scene to give the driver of the truck in the crash an oxygen mask to protect him from the billowing clouds of acid.
"Very bitter in the lungs and dry," he said. "It's very nasty."
Windy conditions spreading those clouds made it difficult for rescue crews to get to the driver.
Refresh WPXI.com for updates on this developing story.