A 16-year-old sophomore boy armed with two knives went on a stabbing rampage inside the science wing of a Pennsylvania high school Wednesday morning, injuring at least 20 people, including two students who were in critical condition, officials said.

“None of these are superficial wounds. These all have significant stab wounds,” said Chris Kaufmann, a trauma surgeon at Forbes Regional Hospital in Monroeville, Pa., which is about seven miles from the site of the stabbing at Franklin Regional Senior High School in Murrysville, Pa., east of Pittsburgh.

Forbes took in eight patients, including some of the most seriously injured, because it is close to the crime scene and has a trauma unit. Kaufmann said seven of the patients there were teenagers and one was an adult.

The adult, whose age was not given, suffered what officials at Forbes described as a “medical condition,” not stab wounds, hospital officials said. The injured were expected to survive. They were stabbed in the chest, abdomen, back or flank, Kaufmann said at a televised news conference.

“Patients who are stabbed in the abdomen and chest have, by definition, life-threatening injuries,” Kaufmann said.

The assailant was in custody, emergency officials said.

The brother of one of injured students, told the Los Angeles Times that his sibling, Jared Boger, a junior, was stabbed in the chest.

“He’s in critical condition but they’ve stopped the serious bleeding,” Carter Boger said in a message.

Alex Carolla said his 17-year-old sister, a senior, was stabbed in the hand and was taken to the hospital.

“She’s stable; she’s OK,” said Carolla, a 19-year-old sophomore at Ohio University, adding, “When I talked to her, she seemed all right, but she got a little more upset when I asked her about the other kids, who else was hurt.”

Carolla said his sister told him that she had just arrived at school when the chaos began; she hadn’t even made it to her locker yet. “I’ve been telling myself this whole morning, she’s so lucky, it could have been worse,” Carolla told The Times.

Murrysville police Chief Thomas Seefeld said at a news briefing that the attack began at 7:13 a.m. on the first floor of the school.

Seefeld described arriving at the campus to see “multiple victims” on the grassy area outside the building.

In the first-floor hallway he encountered a male security guard with a stab wound to his stomach. Police already had the suspect handcuffed in custody. Seefeld said the alleged assailant suffered wounds to his hands and was receiving medical treatment.

One student tweeted that she saw the attack and that the attacker “did not look normal it was unnatural he just stabbed anyone around him,” adding that she then saw people falling to the ground.

The alleged attacker’s name has circulated privately among Franklin students. Shane Molyneaux, a sophomore, told The Times that he knew the attacker.

“He was quiet,” Molyneaux said in a message. “He was very smart and had a good future ahead of him. I do not know what his motive would be because he was not bullied.”

After the attack began, a pupil yanked a fire alarm, causing confusion as hundreds of teenagers were arriving for the start of classes, Seefeld said.

“The juvenile went down a hallway and was flashing two knives around,” Seefeld said.

•Text: Los Angeles Times. Photo (suspect inset): New York Post.

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