"For the show to happen u must all listen to the police. we are all concerned for your safety and i want what is best for u," Bieber, 18, Tweeted, at the behest of authorities, as a horde of fans caused a chaotic scene around the Opera House in Oslo, where the pop star was scheduled to perform a free concert.
He added: "Please listen and tonight we will have some fun. love you and im excited to see you all."
Almost 50 teenage girls were injured in the melee, with 14 taken to the hospital for emergency care, TMZ.com reports.
Still, the show did go on – with Bieber performing his hit "Baby" and four other songs. It had been almost a year since Bieber last performed for a crowd. "Missed the stage. that was fun," he tweeted later. "#BELIEVEtour is gonna be epic."
The singer arrived in Paris on Thursday and was expected to perform another surprise show.
NORWAY - please listen to the police. I dont want anyone getting hurt. I want everything to go to plan but your safety must come first...— Justin Bieber (@justinbieber) May 30, 2012