Police said they are investigating whether it was a terrorist attack. The university asked anyone with information to call police. "Someone said they heard popping right before we got the alert, but I didn't hear it".
Authorities say a man purposely plowed his vehicle over a curb and into pedestrians on Monday morning before jumping out of the auto and attacking people with a butcher knife.
University police said at about 11:30 a.m. that the scene was "now secure", but said they would keep an area on the campus closed.
The FBI and other agencies joined the investigation.
"I thought it was an accident initially until I saw the guy come out with a knife", Schneider said, adding that the man didn't say anything when he got out.
Student Martin Schneider said he heard the car's engine revving. A campus officer nearby because of a gas leak arrived on the scene and shot the driver in less than a minute, Stone said.
Eight people were taken to the hospital, the station reports.
Most of the injured were hurt by the auto, and at least two were stabbed. It was not immediately clear if the sound of an explosion was the vehicle crashing, or something else.
A Somali-born Ohio State University student plowed his auto into a group of pedestrians on campus and then got out and began stabbing people with a butcher knife Monday before he was shot to death by a police officer. Columbus police officers and the Franklin County Sheriff's Office also said they were assisting university police.
"Here in the United States, our most immediate threat still comes from lone attackers that are not only capable of unleashing great harm but are also extremely hard, and in some cases, virtually impossible to identify or interdict", he said.
Shortly after 11 a.m., university officials lifted the shelter-in-place directive and canceled all classes on the Columbus campus Monday.
Authorities said later that it doesn't appear that the suspect used a gun in the attack. The injured were stabbed, hit by a vehicle or suffered other injuries, Johnson said.
A law enforcement official told The Associated Press that the suspect is believed to have initially struck people with a auto before beginning to stab victims. Some then heard gunshots, though the shots might have been fired by police during their pursuit and encounter with the suspect.
The details emerged after a morning of conflicting reports and confusion, created in part by a series of tweets from the university warning there was an "active shooter" on campus and students should "Run Hide Fight".
Associated Press writer Eric Tucker contributed to this report from Washington, D.C.
The bloodshed came as students were returning to classes following the Thanksgiving break and Ohio State's football victory over rival MI, which brought more than 100,000 fans to campus on Saturday. The campus will remain open, but 14 buildings were closed until further notice.
At least eight people have been sent to hospitals.
The fate of any suspect or suspects wasn't immediately clear.
The eight patients were split among OSU Wexner Medical Center, OhioHealth Grant Medical Center and OhioHealth Riverside Methodist Hospital.
Ohio State University says a shelter-in-place warning has been lifted and the scene is secure following reports of an active shooter and at least seven people injured. The Bureau of Alcohol, Tobacco, Firearms and Explosives said Monday it was sending agents from its Columbus division to the Ohio State campus. NBC earlier reported that two were in stable condition and the conditions of the others was unknown. It didn't have details on the other five.
One person was in critical condition, CNN reported, citing the Columbus Fire Department. Then she heard what sounded like five or six gunshots - a familiar sound to her from her small hometown in northeast OH where hunting is common - and sprinted with people to a nearby dorm.
Two people familiar with the case said the suspect is believed to have driven toward a group of pedestrians outside of Watts Hall before emerging with a knife.
A professor reached by telephone said he was told that a colleague in the materials science and engineering department had been stabbed at Watts Hall.
Ohio State's official Twitter page retweeted a post from OSU Emergency Management saying there is an active shooter on campus in Columbus on Monday morning. In the announcement, university officials said that "law enforcement will continue to have a visible presence on campus".
"Run, hide, fight" is standard protocol for active shooter situations. It means: Run away if possible; get out of view; or try to disrupt or incapacitate the shooter if your life is in imminent danger.
The FBI is on scene assisting local police in Columbus.