Twenty people have been injured - some with life-threatening wounds - after an assailant went on a stabbing spree on Wednesday at Franklin Regional High School in Murrysville, Pennsylvania.

According to CNN, a 16-year-old male sophomore student is in custody after running through the hallway on the first floor and into several classrooms stabbing his victims with two knives. Murrysville police Chief Thomas Seefeld confirmed that the suspect is in custody after being wrestled to the ground.

According to Westmoreland County emergency management and hospital officials, nineteen students between the ages of 14 to 17 and one school employee were injured.  Reports stated that seven students and the adult suffered life-threatening injuries. Forbes Regional Hospital in Monroeville, Allegheny General Hospital and UPMC-Presby are treating patients.

Dan Stevens, an emergency management agency spokesman, said that four of the patients were flown to hospitals by helicopter and three were being operated on. All victims are reportedly expected to survive.

Mark Rubino, chief medical officer for Forbes Hospital said the worst injuries included stabbing in the lower abdomen and significantly damaged internal organs. Health officials found wounds in the torso, abdomen, chest and back areas.

"They are deep, penetrating injuries," Rubino said. "The critical nature of these injuries really demanded an acute response."

A student told reporters that the stabbings happened in the science wing of the building. Officials received an emergency call by a resource officer around 7:13 a.m., about 15 minutes after school doors opened for the day. Many students had not yet arrived on campus. Parents were told to report to the town's elementary school to reunite with their children.

Seefeld said the suspect was tackled to the ground by the school principal Sam King, who handcuffed him and waited for police officials to arrive. A witness set off the fire alarm after the attack. The suspect has not been identified, but is currently being interrogated by police.

The New York Daily News reported that the school district posted the following statement on its website:

"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."