Rapper MIA cut her set at the Big Chill festival in Herefordshire short after up to 200 people climbed on stage during her headline appearance.
The Sri-Lankan-born star asked people to join her for her hit Paper Planes.
Festival organisers said MIA apologised for ending the set early, adding that only a few fans were expected to join her.
Some in the crowd complained of a crush as fans rushed on stage. But no-one was badly hurt.
Festivalgoer Laura Graham, from Cheltenham, Gloucestershire, said: "People were sprinting from the back of the crowd to get their moment of glory but the stage was completely full.
'Out of hand'
"Ben, a friend of mine, was standing at the front and had his girlfriend on his shoulders.
"There was this big rush of people trying to climb on to the stage and he said it got a bit hairy as he was being crushed against the railings and couldn't breathe at one point.
"But he also didn't want to let Rachel fall in case she got caught in the crush."
Another fan, Adam Hunt, from Newton St Cyres, Exeter, said: "It was good up until the end. I don't think they should have let so many people on stage - I didn't expect it to get so out of hand.
"A lot of people could have been injured. You had young girls being pushed about and I had 10 year olds, if that, in front of me."
A statement on the festival's Twitter feed said: "A spokesperson for MIA thanked the wonderful audience at the Big Chill for the fantastic reception received and apologised for having to cut the set short due to overwhelming demand for fans to come on stage when only a few were expected."