Donna Svennevik/ABC

Justin Bieber fans got a little more than what they bargained for this weekend when the pop star vomited twice on stage during a concert in Glendale, Ariz.

Video of the incident made its way around Twitter and YouTube following the concert on Saturday at the Jobing.com Arena, which was the first stop on his highly anticipated "Believe" tour. Luckily for the more than 18,000 fans in attendance, Bieber returned to the stage and the show went on without a hitch. The teen pop star even did an encore for fans.

The first instance came when he was singing "Out of Town Girl." Bieber, 18, turned his back to the crowd, hunched over and puked on stage before quickly exiting.

After the second incident, Bieber returned to the stage and told the crowd, "It's hard for me, you know, not feeling great and throwing up in front of a bunch of people," according to USA Today. Bieber asked the crowd, "Will you love me even though I'm throwing up on stage? OK, I wanted to give you my best show ever, so do you mind if I finish it?"

After the show, Bieber tweeted "Great show. Getting better for tomorrow's show!!!! Love u."

"And …. Milk was a bad choice!" he added in another tweet - a nod to the Will Ferrell comedy "Anchorman."

Bieber's 45-city "Believe" tour continued Sunday at the MGM Grand Garden Arena in Las Vegas.