Ohio State University is on lockdown amid reports that an active shooter was at large on the campus in Columbus, with students told to run or take shelter.
The university's website warned students and staff on Monday there was a gunman on campus and they should "run, hide, fight".
Seven people were sent to the hospital on Monday morning, the Columbus Fire Department said.
Two of those people were in stable condition, the department was quoted by the Associated Press as saying. It had no information on the other five people.
It was still unclear if anyone had been shot.
Cassidie Baker, an Ohio State senior, said she saw police or paramedics helping one person on the ground outside Watts Hall, a materials science and engineering building. "No one really knows what is happening, other than there's an active shooter," she said.
Ohio State said about an hour and a half after its initial tweets that a shelter-in-place warning had been lifted and the scene was secure. The university tweeted all classes would be cancelled for the rest of the day.
|Ohio State University [Al Jazeera]
Ohio State's official Twitter page retweeted a post from OSU Emergency Management saying there was an active shooter on the north campus.
Al Jazeera's Rosiland Jordan, reporting from Washington DC, said the situation was ongoing.
"It's not clear whether it's one person or two people at this point. We should note they closed off a large part of the campus. Local reports are saying someone might be surrounded in a parking garage on the campus. But again this is still very much a situation in progress."
An earlier tweet from the university said: "Buckeye Alert: Active Shooter on campus. Run Hide Fight. Watts Hall. 19th and College."
"Run, hide, fight" is standard protocol for active shooter situations. It means: Run, evacuate if possible; Hide, get silently out of view; or Fight, as a last resort, take action to disrupt or incapacitate the shooter if your life is in imminent danger.
A Columbus police dispatcher declined to comment on the reports, but police vehicles were seen at the scene, AP reported.
The university in Columbus followed up with another tweet that said: "Continue to shelter in place in north campus area."
With nearly 60,000 students at its main campus, Ohio State is one of the nation's largest universities.
Source: Al Jazeera News and Agencies