The accident happened along Route 611 (Easton Road) in Ottsville near Tohickon Valley Road at 7:45 a.m
Authorities say a car crossed over the center line and slammed head-on into a Cress Gas Company truck, which was fully loaded with 3,000 gallons of propane.
Both drivers were injured in the crash.
"There's gas ejecting and it ignited and there's a fire so they decided to let the fire continue burning to help relieve the pressure in the tank," emergency management spokesman Martin Focazio said.
Firefighters and hazmat crews worked to keep the tanker cool with foam and water, treating it as a ticking time bomb in the middle of Route 611.
"It's very volatile. At any time the tank could have exploded. If you noticed the trucks were set up, there was nobody with them. We set them up and abandoned them. Let them flow water on to keep it cool," Ottsville Fire Chief Tom Rimmer said.
Officials were so concerned about the danger they evacuated a one mile area around the tanker and set up a shelter for evacuees at St. John the Baptist Church on Durham Road in Nockamixon Township.
Marion Mergenthaler grabbed her dog Lily and headed to the church after fire police knocked on her door and told her to get out.
"I left everything. Whatever I was going to do today I'm not doing. I left because you never know," Mergenthaler said.
"Basically we noticed traffic stopped at 8:00, no customers were coming in or anything. All of a sudden, a gentleman from the fire company said 'we're evacuating the area within a mile radius," said Will Ganley of the Ottsville Post Office.
That order was lifted by mid-afternoon.
There are no hydrants in the area so officials activated what's called the Tanker Task Force. The task force brings in dozens of tankers from counties all around the area to provide water that can then be dumped on the burning propane tank.
Route 611 reopened at around 7:00 p.m.