Justin Bieber treats fans to free concert in Mexico City

MEXICO CITY

The teen idol opened with his hit song "Baby," while some adoring fans sang along and others just shouted "Justin! Justin! Justin!"

More than 5,000 police officers were on hand to keep the girls under control.

The crowd went wild when Bieber asked a fan onto the stage, gave her a bouquet of flowers and sang "One Less Lonely Girl" into her ear. The girl didn't stop crying.

After singing a couple of songs while playing an acoustic guitar, Bieber changed into an all- black outfit and sang some of his more energetic songs, including "Somebody To Love."

The crowd of "tween" girls was a sea of purple - what is reported to be Bieber's favorite color.

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