MERCED, Calif. » A male college student burst into a morning class at a California university with a foot-long hunting knife Tuesday and may have killed his intended victim if not for the heroic intervention of a construction worker who ran into the room to break up the attack.

The construction worker and three others were injured, but all are expected to survive. The alleged assailant, described as a college student in his 20s, was shot and killed by campus police as he fled the scene at the University of California, Merced.

Two of the injured had to be airlifted to nearby hospitals, and the other two were treated on campus. Authorities didn’t release the name of the assailant or his victims.

The incident began when the assailant stabbed two people in a second-floor room around the start of an 8 a.m. class, Merced County Sheriff Vern Warnke said.

A construction worker outside rushed into to check on the commotion, distracted the attacker and was also stabbed. Warnke credited the worker with saving the life of one of the victims.

“I think he prevented this first student from dying,” Warnke said during an afternoon news conference. “He didn’t go in knowing that there was a stabbing taking place. He went in thinking there was a fight.”

The Merced County Star identified the construction worker as Byron Price, 31. Price’s father said he was treated and released from the hospital. Neither Price returned calls for comment.

Warnke said the suspect fled the room after attacking the construction worker and ran down two flights of stairs to the building’s lobby, where he stabbed a school employee sitting on a bench. The suspect fled the building. He was shot and killed by pursuing campus police on a nearby bridge.

Authorities didn’t discuss a motive.

All the victims were conscious when paramedics reached them, Assistant Vice Chancellor Patti Waid said. The two victims who were airlifted were brought to hospitals in Modesto, but their conditions were not immediately known. The three others had injuries that were minor enough that they could be treated on campus, Waid said.

Campus officials said the assailant was a student, but they had not confirmed his identity or provided a motive for the attack.

University senior Phil Coba, a student government representative, said numerous students told him that the stabbings started inside a classroom and continued outside before campus police shot and killed the attacker.

Lensy Maravilla, 19, a first-year student, said she was in a biology class on the second floor of the same building, when a female student ran in.

Maravilla said the student “was crying hysterically and came in and said that she had seen somebody get stabbed, or slashed, in the throat and she ran.”

Maravilla did not have other details, but she said that shortly afterward someone came in the class and said classes were canceled.

Student Itzel Franco, 18, said half of her dorm remains evacuated because it is close to the site of where the assailant was shot. She said it happened in an area known as the “passing bridge.”

Student Alex Lopez was heading to class when he realized something was wrong on campus. “I was listening to a podcast, and there was a break in talking, and I just hear a gunshot,” he said.

He said police and first responders flooded the scene.

“You see this stuff all over the news and stuff, and you see it happen to all these other schools,” but you don’t expect it to happen at your school, said Lopez, 21.

The university about 120 miles south of Sacramento in the farm-rich San Joaquin Valley was locked down for about an hour and a half after the stabbings. The lockdown was lifted, but classes were canceled and entrances to the campus were blocked off.

Campus officials said the university, which has about 6,000 students, also would be closed Thursday and urged the community to seek counseling services that were available.

The campus in the city of Merced opened a decade ago and is the newest one in the University of California system.

It was erected in the state’s farm belt in response to the burgeoning enrollment in the nine other University of California campuses. Regents also felt the mainly agricultural region was unrepresented by higher education.

___

Elias reported from San Francisco. Associated Press writer Lisa Leff contributed to this story.