A man drove a sport utility vehicle into a crowd of pedestrians at Ohio State University, in the US, this morning then jumped out and stabbed several people with a butcher's knife, injuring at least nine, officials say.
A police officer shot and killed the assailant within a minute of the attack beginning, Ohio State University police chief Craig Stone said.
A US government source said investigators had reason to believe the attacker was a Somali refugee. The city has a large Somali population.
Local officials declined to say what might have motivated the attack, and gave no details about the assailant, including his identity or whether he was a student at the university.
The man jumped the curb and used the vehicle to strike pedestrians in front of Watts Hall, Monica Moll, the university's director of public safety, said at a news conference. Local media reported the attacker used a sport utility vehicle.
He then left the vehicle armed with a butcher's knife and stabbed several others, Mr Stone said.
"The only thing that you can say based upon common knowledge is that this was done on purpose,"he said. "To go over the curb and strike pedestrians and then to get out and start striking them with a knife, that was on purpose."
One person was critically injured, a Columbus Fire Department spokeswoman said. There were differing accounts on the total number injured. The fire department reported 10, while officials at a press conference said nine.
The alert began at around 10am local time when the college warned students in a tweet to "Run Hide Fight".
Buckeye Alert: Active Shooter on campus. Run Hide Fight. Watts Hall. 19th and College.— OSU Emergency Mngmnt (@OSU_EMFP) November 28, 2016
Hours later police declared the scene "secure", lifting the shelter-in-place order and cancelling classes for the remainder of Monday.
Columbus Police tweeted that they had sent a SWAT team, dog units, negotiators and a helicopter to the scene.
Federal officials from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives also responded.
"The first thing I heard were screams," student Cydney Ireland told ABC News.
"Probably five seconds after that there were three gunshots and it sounded like a handgun.
"And I've never seen anything like it. Everybody was running in any direction they possibly could."
According to the school newspaper, The Lantern, police surrounded the Lane Avenue parking garage, where an officer at the scene said the suspected attacker was believed to be inside.
A bomb squad was also at the scene, the newspaper reported.
Facebook activated a safety check feature, allowing people nearby to post their status regarding this "violent incident".
Nearby public school districts also placed their students on lockdown.
"Ohio's thoughts and prayers go out to the Ohio State community," Ohio Governor John Kasich tweeted.
"Be safe, listen to first responders", he added.
The Columbus-based university, which has 60,000 students, is one of the largest in the US.