Police were called to control crowds waiting for a Tyler, The Creator concert in Colorado on Monday after a riot broke out.

Fans were queuing for first-come, first served tickets to the rapper's solo show at the Fox Theatre in Boulder, but the 2,000-strong line began to spiral out of control hours before the gig was due to start.

A local businessman was allegedly assaulted by an intoxicated fan and at least one man was arrested in the chaos, according to local reports.

The rapper attempted to calm the situation by announcing plans for an additional gig at the venue.

In a post on his Twitter page, he wrote, "Two shows tonight so everyone can come guys."

Speaking about the situation, operational manager of Fox Theatre Brian Carp says, "This is the reason we normally don't do free shows."