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 showed the pop star vomiting twice on stage on 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 managed an encore.
KTVK reported Justin's fans sang some of his songs while he was offstage and he later apologised for being sick.
Justin later tweeted: "Great show. Getting better for tomorrow's show!!!! Love u."
He later added: "And ... Milk was a bad choice!"
Justin's 45-city Believe tour continues at the MGM Grand Garden Arena in Las Vegas.