Discuss as:

Justin Bieber throws up on stage during Arizona concert

Justin Bieber's "Believe" tour is off to a rocky start. TMZ obtained a video of the 18-year-old singer getting ill while performing  at the 18,000-seat Jobing Arena in Glendale, Ariz., on Saturday. The clip shows Bieber turning his back to the audience while singing "Out of Town Girl," then hunching over, puking and running to the side of the stage.

VIDEO: Behind the scenes with Justin Bieber

When he returned, Bieber powered through the rest of his set. "It's hard for me, you know, not feeling great and throwing up in front of a bunch of people," he said. "Will you love me even though I'm throwing up on stage?"

After the sold-out crowd shrieked, he responded, "OK. I wanted to give you my best show ever, so do you mind if I finish it?"

PHOTOS: A-listers with Bieber fever!

Bieber later dedicated the song "One Less Lonely Girl" to Avalanna Routh, the 6-year-old fan who died of cancer Sept. 26. "If you're listening, I love you," he said, looking up.

PHOTOS: How Justin Bieber stays in shape

Despite his illness, Bieber tweeted that it was a "great show" and promised he was "getting better" before his Sunday concert in Las Vegas. "And milk was a bad choice," he tweeted.

Related content: