Justin Bieber
The multi-millionaire\'s string of disturbing antics has sparked concern.

Justin Bieber's increasingly wild antics have sparked concern among fans that he could be spiralling out of control.

The teenage pop sensation, whose catalogue of unusual - for him - behaviour includes smoking marijuana, excessive partying and being late for his own concert has shocked fans.

One source told the Sun: "Justin's been going off the rails in recent months. He's bound to be pulled in for crisis talks."

The Baby star was on the receiving end of a backlash by fans and furious parents after turning up late for his sold-out concert at London's O2.

The delay, which many said showed a lack of respect for the people who pay his wages, forced hundreds of fans to leave the gig early in order to catch the last train home.

He made a grovelling apology on Twitter and blamed technical issues, while still insisting he had been only 40 minutes late for his set.

"There is no excuse and I apologise for anyone we upset," he said on Twitter.

But it has emerged that the star was apparently larking around backstage and threw a tantrum after staff pleaded with him to start the show.

One concert worker said: "He was arguing with members of his management, his family. It was a really uncomfortable atmosphere. His attitude was, 'I'm the star and I can do what I want.'"

Bieber also allegedly blanked a 15-year-old competition winner who won the chance to meet him before the gig. He is said to have spent only 10 seconds with her and said he did not have time when she asked for a cuddle.

The 19-year-old heartthrob has courted more controversy since Christmas.

In January he made headlines when pictures of him smoking marijuana with a friend during a party in Newport Beach surfaced online.

The images sparked accusations that he was setting a bad example for his young fanbase.

Since arriving in the UK for his tour, has been snapped in the capital wearing strange outfits including a gas mask while out shopping and going bare-chested in freezing temperatures.