JOHANNESBURG (AP) — South African media are reporting numerous muggings after a charity concert at which Beyonce and other international stars performed.

People said on social media on Monday that they saw thugs attacking concert-goers and grabbing cell phones after the music festival at FNB Stadium in Johannesburg. The event on Sunday honored Nelson Mandela a century after he was born and highlighted campaigns for girls' education and other causes.

Organizers of the Global Citizen Festival: Mandela 100 tweeted that they are "saddened to hear the challenges people had while leaving the venue," and that they were working to help people get home safely.

A reporter for eNCA, a South African news organization, says muggers in one area outside the stadium "were basically having a field day" because police were not present.