A teenager armed with two knives has gone on a rampage at a high school in the US state of Pennsylvania, injuring 19 students and asecurity guard.
The 16-year-old student was taken into custody at Franklin Regional High School in Murrysville, a suburb of Pittsburgh, police said.
The wounded, some with serious stab wounds to the torso, were as young as 14. Several were in surgery in hospital.
All are expected to survive.
Eight patients were transported to nearby Forbes Regional Hospital, three of whom had suffered severe injuries.
Two of those patients were in critical condition, while up to four were expected to recover from superficial wounds, Dr Mark Rubino told reporters.
The school will be closed for the next several days as investigators process the crime scene, Gennaro Piraino, superintendent of the Franklin Regional school district said.
"Our thoughts and prayers are with the injured and all of those affected by this awful tragedy," he said. "I pray and we pray every day that this doesn't happen."
The initial report of the attack came before 08:00 local time (12:00 GMT) on Wednesday morning.
"A critical incident has occurred at the high school," school officials wrote in a bulletin. "All elementary schools are cancelled, the middle school and high school students are secure."
The panicked students poured out of the school building, some suffering injuries in the chaos, as police descended in search of the suspected attacker.
Among the injured was a security guard, Murrysville Police Chief Thomas Seefeld said.
Morris Hundley said his "frantic" 14-year-old daughter Morriah called him to say a friend of hers had been stabbed at the school in Murrysville.
"She needed me or my wife to come get her," he said. "She was just frantic, I never heard her talk like that."