At least nine people were injured Monday when a man drove into a crowd of students at Ohio State University and then emerged from his vehicle to attack bystanders with a butcher knife, officials said.

The unidentified attacker was shot and killed by a university police officer who was on the scene within a minute, campus police chief Craig Stone said at a news conference.

“Commands were not followed and the officer did what he had to do to end the threat,” said Stone. He declined to give a possible motive for the attack other than to say, “This was done on purpose.”

Nine victims were taken to three local hospitals, but none of the victims’ injuries were considered life-threatening, said Andrew Thomas, the chief medical officer for the Ohio State University Wexner Medical Center in Columbus.

Four of the victims had knife-related injuries and four had injuries related to being hit by a vehicle, Thomas said. A ninth victim came forward later because she had been “hiding in place,” Thomas said.

Footage from the campus student news outlet, The Lantern, showed a young woman walking toward an ambulance with a pair of medical officials, holding what appeared to be an injured arm elevated in the air.

The attack happened at about 9:52 a.m., and less than five minutes later, university officials sent out a warning to students on campus: “Active Shooter on campus. Run Hide Fight.”

Police later said that the attacker did not appear to have a gun and that he appeared to have acted alone.

“The guy ended up just coming and hopping the curb with his car and trying to mow down a couple people,” Jerry Kovacich, a third-year student in welding engineering, told The Lantern. “He lost control, and I think he ended up hitting three people, and then people were around the car. Somebody asked him if he was OK and the guy just hopped out of the car with a butcher knife and starting chasing people around.”

An Ohio State University police officer was on the scene “in less than a minute and ended the situation in less than a minute,” said Stone.

“We believe injuries were minimized as a result of that,” said Monica Moll, the university’s public safety director.

The attack prompted a campus lock-down as police searched the area for possible other suspects, but the shelter-in-place order was lifted less than two hours later.

With nearly 60,000 students at its main Columbus campus, Ohio State is one of the nation’s largest universities.