Ambulance (illustrative)
Ambulance (illustrative) Thinkstock

At least 20 people have been injured in a stabbing spree at a high school in Pennsylvania.

Local police say they have apprehended a suspect, a 16-year-old student at the school, who is believed to have carried out the attack in Westmorland County after entering school premises with a large knife.

All those wounded are believed to be students as well, and at least seven of them are "life-threatening" injuries, according to NBC News.

The motive in the brutal attack is not yet know.

The Franklin Regional School District's website has posted a notice, simply stating: A critical incident has occurred at the high school. All elementary schools are cancelled, the middle school and high school students are secure. Additional information will be released as soon as possible. Please keep our campus clear of traffic.