Rockers Rage Against The Machine stopped their performance at the Lollapalooza festival three times on Saturday when surging crowds threatened to crush fans nearest the stage.

Thousands of revellers flocked to watch the band headline the event in Chicago, Illinois - including a number who had broken into the venue by hopping over fences.

The crush was so severe, singer Zack De la Rocha stopped the gig after three songs to plead with fans to step back. Later he paused again to consult with security bosses.

It's unknown if any injuries were suffered during the performance, but MTV reports at least 12 people were admitted to the medical tent.

Local newspapers have reported at least one breach of the venue's perimeter fence.

Rage Against the Machine were joined at Lollapalooza by Chicago native rapper Lupe Fiasco and Kanye West, who closed the event on Sunday night.