Initial reports broadcast by local television say that the attacker went through the high school's halls acting "crazy" and stabbing as many students as he could before he was overpowered.
Several of the injured were taken to medical centers by helicopter with eight of them being transported to the Forbes Regional Hospital in Monroeville with stab wounds, Pittsburg's Channel 4 TV reported.
Forbes Hospital physician Mark Rubino said that three of the students required surgery and two are in critical condition. Other medical authorities said that at least seven people were seriously injured with cuts and penetrating wounds in the chest and abdomen.
US President Barack Obama sent a message of solidarity to the relatives and victims of the attack from Texas, where he is attending the funeral services for the victims of the shooting attack last week that left four people dead and 16 wounded on the Fort Hood military base.
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