The crowd of several thousand Australian Justin Bieber fans moved from the initial concert site of Circular Quay to Sydney's Martin Place in front of the Channel Seven studios to see the teen pop star. (Graham Denholm/Getty Images)

Overzealous fans forced Australian police to cancel teen pop star Justin Bieber's free performance in Sydney on Monday morning, after several young people were crushed and trampled by the surging crowd awaiting him.

The chart-topping Canadian entertainer had been set to perform a three-song set outside the Overseas Passenger Terminal at Sydney's Circular Quay as part of an appearance for Sunrise, a show on local network Channel Seven.

Amid rumours that Bieber had arrived early for the show, fans began gathering at the site on Sunday evening. By 3 a.m. local time Monday, police estimated that a crowd of more than 3,000 fans — mostly young teenage girls — were pushing up against the safety barriers. The number later grew to an estimated 5,000 fans.

Several of the onlookers were crushed as the growing crowd breached the barriers and police decided to cancel the performance. According to reports, eight fans were taken to hospital for minor injuries, while dozens of others were treated on-site for hyperventilation.

The 16-year-old Bieber posted a message about his disappointment at the cancellation on Twitter.

"I woke up this morning to the police cancelling the show for safety reasons," he wrote. "I love it here in Australia ... and I want to sing."

'We had 12-, 13- and 14-year-olds [alone] at 3 and 4 a.m. in the morning. They were being crushed up against the barrier.'—Dave Owens, deputy police commissioner

Bieber later performed one song from inside the Channel Seven studios, where many fans had migrated after the cancellation of the Quay concert, billed as the teen star's sole Australian performance.

Police blamed lack of parental supervision and the disorderly crowd for the crush, with Deputy Police Commissioner Dave Owens describing the situation as out of control.

Justin Bieber, right, stands with a Channel Seven personality. After his original three-song outdoor concert in Sydney was cancelled early Monday, he performed one song from inside the Channel Seven studios. (Graham Denholm/Getty Images)

"There were a number of parents down there [but] I would question why there weren't a larger number of parents," he told Australian press.

"We had 12-, 13- and 14-year-olds [alone] at 3 and 4 a.m. in the morning. They were being crushed up against the barrier... They wouldn't abide by our directions. They left us with no option [than to cancel]."

Channel Seven defended the security hired for the show.

"We hired the professionals who look after U2, Coldplay, Pink — the big acts," Sunrise weather presenter Grant Denyer told the Australian Broadcasting Corporation.

"Even they weren't equipped and just couldn't handle the Bieber fever."

In March, Bieber's manager, Scott (Scooter) Braun, surrendered to New York police over a similar incident in 2009 where fans gathered for a mall performance grew into an unruly throng.

New York police cancelled that event because of the wild, disorderly crowd, and allege that Braun and a record label executive delayed relaying a Twitter message to fans that the show had been cancelled.

Stratford, Ont.-born Bieber, who rose to fame after posting videos of himself singing on YouTube, released his first album, My World, in November 2009. His followup album, My World 2.0, debuted in March.