Several girls injured at Justin Bieber event

Live performance canceled after crowd got out of control

SYDNEY -- New Zealand is tightening security for a visit by Canadian pop star Justin Bieber after a live performance by the teen singer in Sydney had to be canceled when a 5,000-strong crowd of young girls ran out of control.

Thousands of mainly tween girls had camped out overnight to catch up a glimpse of their 16-year-old idol, who was due to sing three songs live at Sydney's Circular Quay on Monday morning for an Australian TV show.

But police were called in as the crowd got out of control before the singer arrived and several girls were injured in the crush and others fainted, sparking comparisons to the reaction of young fans when The Beatles went on tour in the 1960s.

"With everything that happened 2day i want u all 2 know that i care and U all rule and if i could thank every 1 of u individually i would," Bieber wrote on his Twitter account.

Bieber, who is in Sydney to promote his album "My World 2.0," is due in New Zealand later this year and officials from Auckland Airport told the New Zealand Herald newspaper that extra security would be arranged for the singer's arrival.

It's not the first time that Bieber has sparked such a reaction.

In March an appearance by Bieber at a U.S. shopping mall was canceled due to overcrowding. Bieber's manager was arrested for refusing to send a message out on Twitter warning fans not to come to the event.

Bieber shot to fame after being discovered on YouTube where his mother had posted videos of him singing at talent shows. He was signed up by rapper Usher's record label Island Def Jams Music Group at the age of 14.

His "My World 2.0" album hit the No.1 spot on the Billboard charts in the United States within a week of its release last month.