A community college was briefly placed on lockdown Tuesday after a telephone report of an armed man on the Southern California campus.

Dozens of heavily armed police swarmed the college shortly after calls came in around 11 a.m.

At least one student had apparently heard shots on campus. One girl was on the phone with her mother when she heard the noise. The mother alerted authorities in Riverside County, who in turn called the college.

After an extensive search of the campus, it was determined there was no gunman or any evidence of a gunshot. The lockdown was lifted within 90 minutes.

It was not immediately clear what noise the callers may have mistaken for gunfire.

The college is a two-year community college with about 30,000 students. School was not in session but some summer classes were taking place, and teachers and some incoming freshmen were on the college grounds.

School spokesman Bruce Smith said the college sent an email to all employees about the lockdown.