Pittsburgh school stabbings: 20 students injured in mass knife attack spree at US high school

All victims at Franklin Regional High School were between 14 and 17 years old, police said

Police said 20 students were injured in the attack outside Franklin Regional High School in Murrysville, near Pittsburgh this morning (ABC News)

Up to 20 people are reported injured following a stabbing spree at a US high school.

Police at Franklin Regional High School near Pittsburgh, Pennsylvania, said four students were seriously injured, with the majority of the rest of the victims also suffering puncture wounds.

Local media reports suggested the attack took place as the school's pupils arrived for lessons this morning, and that victims suffered stab and slash wounds as they scattered from the area around the school gates.

No fatalities have been reported, and according to Westmoreland County's emergency management spokesman Dan Stevens not all of those hurt had been cut by the knife.

All of those injured were between 14 and 17 years old, Mr Stevens said.

A suspect, reported to be a male student, has been taken into custody and was being questioned by police.

Dr Chris Kaufmann, the director of the trauma centre at Forbes Regional Hospital, Pennsylvania, said it had received eight of the victims, with an additional four students taken to another hospital nearby.

He told CNN the injuries were "significant", and said three of the students at Forbes had been taken straight to the operating table. Two of the three were described as not being in a stable condition, after losing significant quantities of blood.

Mr Stevens confirmed the attacker had used a knife, but could provide no details about what kind or any apparent motive.

A message posted to the Franklin Regional School District's website said all its elementary schools had been put on "lockdown".

Mary Catherine Reljac, of the Greater Pittsburgh area department of education, wrote: "After a critical incident at Franklin Regional Senior High School this morning, the campus was locked down.

"Elementary classes were cancelled and high school students were evacuated to the middle school. Law enforcement are working with the school district to manage the situation."