GLENDALE, Ariz. -- It wasn't just Justin Bieber's fans who had "Bieber Fever" as the teen idol kicked off his national tour in suburban Phoenix.

Video posted on KTVK-TV's website shows the pop music star vomiting twice on stage Saturday night during his sold-out concert at the Jobing.com Arena in Glendale. He left the stage after each episode but returned and even did an encore.

KTVK reports (http://bit.ly/W266wZ ) Bieber's fans sang some of his songs while he was offstage and he later apologized for being sick.

Bieber later tweeted "Great show. Getting better for tomorrow's show !!!! Love u"

He later added: "And .... Milk was a bad choice!"

Bieber's 45-city "Believe" tour continued Sunday at the MGM Grand Garden Arena in Las Vegas. He is scheduled to play Los Angeles on Tuesday and Wedneday, Fresno on Friday, and Oakland's Oracle Arena on Saturday.

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Information from: KTVK-TV, http://www.azfamily.com/