Up to 20 people stabbed at Pennsylvania high school

Franklin Regional High School is located outside Pittsburgh, Pennsylvania

As many as 20 students have been stabbed at a high school in the US state of Pennsylvania, authorities have said.

One suspect believed to be a student is in custody at Franklin Regional High School in a suburb of Pittsburgh, a local affiliate of ABC Newsreports.

The wounded, some with significant injuries, range in age from 14-17 and have been taken to area hospitals.

The school was locked down as police searched the premises.

"A critical incident has occurred at the high school. All elementary schools are cancelled, the middle school and high school students are secure," school officials wrote in a bulletin following the incident on Wednesday morning.

Television images of the scene showed students standing in groups outside the school with ambulances nearby.

A parent of a student told CBS television his "frantic" daughter called him to say a friend of hers had been stabbed at school.

"I would never expect this to happen," he said, adding that he had believed the community to be safe.

No information is yet available on the suspect.