Five teenage girls were injured at a free gig performed by The X Factor boyband finalists JLS.
The fans were hurt as 2,000 people gathered for the concert in Croydon, south London.
People were reportedly pushed forward as the crowd swelled when children gathered for tickets after school.
The London Ambulance Service said four of the girls were taken to hospital after their crews were called to the scene.
“We treated five patients. They were all teenage girls, all with minor injuries. Four of them were taken to Mayday Hospital in south London. There was one with a hand injury, one with difficulty in breathing and two who were also just taken unwell. The fifth was treated at the scene,” said a spokesperson.
One concert-goer told the Croydon Guardian she was helped from the crowd after suffering an asthma and panic attack.
“I’d been queuing since 1pm, but when the schoolkids turned up it became so busy with them all pushing us towards the front,” she said.
“There was a pregnant woman in the crowd. It was horrible. I couldn’t move. I couldn’t get out.”
A Metropolitan Police spokesman said: “It was all over and done with by 8pm.”