Three pupils shot and wounded outside Pennsylvania high school

One of the victims is loaded into an ambulance near Brashear High School in Pittsburgh (AP)

A manhunt is underway after three pupils were shot outside a Pennsylvania high school in the United States.

Police told the Pittsburgh Post-Gazette newspaper that three men dressed in black had been reported firing in the direction of Brashear High School from a hill above it as children left for the day at about 2.50pm local time.

Six people were taken in for questioning, but police said they were not being held as suspects.

It is believed the shooting might stem from a drug-related fight between some students last month, police spokeswoman Diane Richard said.

The victims, two aged 17 and one aged 16, had not immediately spoken to or cooperated with police, she said. All were listed in good to stable condition in hospital.

They were hit while walking to a vehicle that had dropped them off earlier in the day, Pittsburgh school district spokeswoman Ebony Pugh said.

She said two were grazed in the head and one was shot in both the foot and arm.