Alex Hribal, 16, is accused of stabbing and slashing 21 students and a security guard in the halls of the Franklin Regional High School in Murrysville, Pennsylvania.

At least five students were seriously wounded in the attack, including a boy whose liver was pierced by a knife thrust which narrowly missed his heart.

Other students suffered deep abdominal puncture wounds in the attack, which took place at 7.13am local time on Wednesday.

The school was locked down during the attack and students were kept inside while officials checked the premises.

Hribal was taken to hospital for treatment to a minor hand wound after he was tackled to the ground by the school's assistant principal, Sam King.

The attack took place at Franklin Regional High School in Murrysville

Police have charged the teenager with four counts of attempted murder and 21 counts of aggravated assault.

A motive has not been established, but authorities are investigating reports of a threatening phone call between the suspect and another student.

During a brief court appearance on Wednesday, Hribal was jailed without bail. Authorities say he will be prosecuted as an adult.

District attorney John Peck told the hearing that after he was seized, Hribal made comments suggesting he wanted to die.

Defence attorney Patrick Thomassey described him as a good student who got along with others, and asked for a psychiatric examination.

While several stabbing rampages have occurred at schools in China over the past few years, however US schools have concentrated their emergency preparations on shooting rampages.