In an update just before 5 p.m., USC said the Los Angeles Police Department concluded its search of both the Leavey and Doheny libraries and declared them safe. As a precaution, both libraries will remain closed until Monday morning.
The alert was first issued at 2:45 p.m. In a post on X, the university said, "A bomb threat was reported at Leavey & Doheny Memorial Libraries at University Park Campus. Stay away from the area."
USC's Department of Public Safety Chief David Carlisle said a staff member received an email saying there was a bomb in either Leavey Library or Doheny Library on campus. He said the source of the email was unknown.
"USC's Department of Public Safety notified LAPD who has taken over the investigation. As a precaution both libraries have been evacuated and are being searched. DPS alert sent out to students at 3:55 p.m. urges students to stay away from the area during the ongoing bomb threat investigation," Carlisle said in a statement.
In an Aug. 27 report, ABC News said nearly a dozen school shooting hoaxes at universities have been reported across the country in the past week, with at least 10 of those believed to be connected to a single group, according to an intelligence report.
While these particular hoaxes, also known as "swatting calls," ended up being false alarms, experts note that these types of hoaxes are not only a serious crime with substantial penalties for those involved, but can also put first responders and bystanders at risk.
"Swatting is not a benign endeavor. Law enforcement is taking it seriously... when they are identified, they are arresting them and prosecuting them," said John Cohen, an ABC News contributor and a former acting undersecretary at the Department of Homeland Security.
The nature of the USC bomb threat is unknown.
ABC News contributed to this report.