"15 injured. They're being attended to by medics," Oslo police wrote on Twitter, adding: "No reports of serious injuries."
Around 1,800 students from the Norwegian Business School were attending a show by American house DJ Steve Aoki at the Sentrum Scene venue when the accident happened.
"The ceiling fell in and it was total chaos. The fire alarm sounded right away," a student attending the concert, Charlotte Nilsen, told news agency NTB.
Police evacuated the building immediately and cordoned off the area while fire officials secured the site.