Three police officers have been killed and two injured in a shooting in southern Pennsylvania.

The shooting erupted in a rural area 185 kilometres west of Philadelphia, not far from the Maryland line, police say.

"We grieve for the loss of life of three precious souls who served this county, served this commonwealth, served this country," Pennsylvania Governor Josh Shapiro said.

"This kind of violence is not OK, we need to do better as a society," he continued.

York Hospital said it was treating two people in serious condition and had enhanced security protocols in place.

"The grief will be unbearable but we will bear it," Pennsylvania State Police Commissioner Christopher Paris told a news conference, who said the shooter is also dead.

"We will not rest until we conduct a full, fair

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