Orem, Utah - Charlie Kirk, a far-right activist and ally of President Donald Trump, was reportedly shot during an event at a college campus on Wednesday.

Kirk was at Utah Valley University when the attack happened. His condition was not immediately clear.

Video from the scene appeared to show Kirk speaking under a tent in front of perhaps a few thousand people when the sound of a single shot can be heard.

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The footage shows Kirk appearing to collapse in his chair before the camera swiftly moves, and the sound of panic begins to erupt in the audience.

"We must all pray for Charlie Kirk, who has been shot. A great guy from top to bottom. GOD BLESS HIM!" Trump wrote on his Truth Social social media platform.

Christine Nelson, from Utah Valley University police, confirmed only that "we did have shots fired. We've asked people to shelter in place."

An alert sent to students said one person was being detained.

"A single shot was fired on campus toward a visiting speaker. Police are investigating now, suspect in custody," the alert said, according to Deseret News.

Former Utah congressman Jason Chaffetz, who was at the rally, told Fox News the shooting had happened during a question-and-answer session.

The person who fatally shot Kirk on Wednesday is still on the run, Utah Valley University said.

"We currently don't have a suspect in custody. This is an ongoing investigation," Ellen Treanor, a spokesperson for Utah Valley University, told AFP.

Trump has ordered US flags flown at half-mast through the week to honor Kirk.

"In honor of Charlie Kirk, a truly Great American Patriot, I am ordering all American Flags throughout the United States lowered to Half Mast until Sunday evening at 6 P.M.," Trump posted on his Truth Social platform.

In a Truth Social post, Trump announced that Kirk had died following Wednesday's shooting.

"The Great, and even Legendary, Charlie Kirk, is dead," the president wrote. "No one understood or had the Heart of the Youth in the United States of America better than Charlie.

"He was loved and admired by ALL, especially me, and now, he is no longer with us."

"First question was about religion. He went on for about 15-20, minutes. Second question, interestingly, was about transgender shooters, mass shooters, and in the midst of that, the shot rang out," a shaken Chaffetz told the network.

"Now I happened to be watching Charlie. I can't say I saw blood. I can't say I saw him get shot, but as soon as that shot went out, he fell back.

"Everybody hit the deck, everybody... a lot of people started screaming, and then everybody started running."

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At only 31, Kirk has an outsized influence in US politics, helping the rise of Trump's support among younger voters – one of the key factors in the Republican's return to power last year.

With natural showmanship skills, Kirk co-founded Turning Point USA in 2012 to drive conservative viewpoints among young people, turning him into the go-to spokesman on television networks and at conferences for the youthful far-right.

He has used his enormous audiences on Instagram and YouTube to build support for anti-immigration policies, outspoken Christianity, and viral takedowns of hecklers at his many campus events.

His presence on campuses is seen on the right as a welcome contrast to widespread liberal viewpoints in higher education, but have sparked often fierce opposition.