Police on Saturday were investigating reports of a gun sighting at the University of California, Irvine during a chaotic scene that unfolded after an ongoing concert was canceled.

The commotion started at the Bren Events Center as the rapper Famous Dex was performing during Shocktoberfest, an annual student-organized event that drew about 4,500 people on Friday night. Doors opened at 7 p.m., according to the event website.

Concertgoers started going up the stage when Famous Dex went into the crowd, UC Irvine spokesman Tom Vasich told KTLA.

According to the campus newspaper, New University, attendees rushed the floor after Famous Dex jumped into the crowd, causing a stampede.

"I just shut the show down...It was all positive vibes," the rapper said on Instagram.

The "unsafe situation" prompted campus police to cancel the event and asked the students to leave the venue in an orderly manner, Vasich said.

"Everyone got pissed off," a student named Jason told KTLA.

He said after leaving the concert, he heard screaming and saw a crowd surrounding Famous Dex's car.

The rapper and his entourage had gotten into his vehicle after the show, Vasich said. Students reported that at some point, somebody from inside the car started brandishing a gun, the spokesman added.

Footage shows students running toward a moving white vehicle with at least two people on top of it.

One student who was on the vehicle  reported witnessing one of the rappers' companions pop out of the sunroof and pull out a gun, demanding the students get off, New University reported.

In a tweet shortly before midnight, UC Irvine police alerted students about an armed 25-year-old man spotted near Pereira and Peltason drives and asked anyone who sees the white vehicle he was in to call 911.

In a follow-up tweet posted 45 minutes later, the agency announced the campus was "all clear" and that officials believed the vehicle had left the area.

The incident drew a large response from police and other officials. Vasich said two people were arrested for public intoxication and that police continued to investigate reports that somebody had waved a gun from inside Famous Dex's vehicle.