NEARLY 50 teenage girls were injured during Justin Bieber's concert in Norway on Wednesday.

Forty nine girls had to be treated - 14 taken by ambulance for emergency care in Oslo, the country's capital - as the 'Boyfriend' star made his first of a number of unscheduled free appearances across Europe.

According to TMZ.com the city was nearly forced to declare a state of emergency as fans swarmed the streets with the hope of catching a glimpse of the Canadian star performing at the Opera House.

Justin tweeted ahead of the performance: ''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. 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 (sic).''

Justin's manager, Scooter Braun also expressed his concern for fans, tweeting: ''The streets are filled...the bridges are closed. it is out of control. we may have to start the show early or they will cancel (sic).''

No one was seriously injured, but Mayor Fabian Stang is planning an investigation.

He said: ''I have already called on the Emergency Planning Agency to examine the entire event from the planning stage to its implementation. We have to find out what went wrong and why it happened.''

Justin was led away from the concert on a police boat after his performance.