It happened around 2:15 a.m. when a driver lost control on a curve on Black Rock Road and 2nd Avenue in Upper Providence Township.
Police say the vehicle ran off the road and struck a tree head-on, trapping the four people in the car.
Fire crews worked to free the victims. Three were taken by helicopter to Penn Presbyterian Medical Center.
The fourth victim was taken to the hospital with not life-threatening injuries.
Police are investigating the crash.
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