Video from local news stations shows a casket that had not yet been lowered to the ground and a crowd of people scattering among gravestones amid the commotion.
Two adults were shot, police said. One was pronounced dead at the scene, and the other was taken to a hospital with life-threatening injuries. Another person reporting chest pains also was taken to a hospital.
Nearby Lansdowne High School was placed on lockdown, but it has since been lifted.
Police have not offered a motive in the shooting or information about the gunman. The victims’ name will be released pending family notifications.
Detectives are looking into the possibility that there was more than one shooter, said Officer Jen Peach, a spokeswoman for the police department.