MURRYSVILLE, Pennsylvania — Four students were believed to be seriously injured at a high school near Pittsburgh, where a student with a knife stabbed or slashed others, injuring as many as 20.

Westmoreland County emergency management spokesman Dan Stevens said not all of the 20 injured were cut by the knife, though most were. Some suffered scrapes and cuts in the mayhem that ensued at Franklin Regional High School outside Pittsburgh on Wednesday morning.

Dr. Chris Kaufman said some victims have suffered injuries classified as life-threatening, though all are expected to survive. He said two victims were in the operating room and one was awaiting surgery.

The suspect, a male student, was taken into custody and being questioned.

It wasn’t immediately clear if the suspect and the victims are students, adults or a mix of both.

School officials and Murrysville police didn’t immediately return calls seeking further details, but the school issued a bulletin on its website saying: “A critical incident has occurred at the high school. All elementary schools are canceled, the middle school and high school students are secure.”

The district serves about 3,600 students. The elementary and middle schools are part of the same campus.

The high school was on lockdown, and students were being kept there as a precaution as school and law enforcement officials double-checked the premises. School officials were making arrangements to bus the middle school students home.

District Attorney John Peck said he was monitoring the situation. Detectives from his office were also investigating, though Peck said he had no information beyond that being reported by Pittsburgh television news stations.

Copyright 2014 The Associated Press.