According to WTAE-TV, eight patients - one adult and seven teenagers - were airlifted to a hospital in Monroeville, Pa.
Other victims were taken to multiple Pittsburgh area hospitals.
A doctor told CNN that some of the injuries are life threatening, with four victims in critical condition.
Police responded to the scene at Franklin Regional High School in Murrysville, Pa., along with multiple ambulances and three helicopters, the ABC affiliate reported.
Police say that one person is in custody, who's identity has not been revealed.
More details are available on WTAE-TV’s website.
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