Justin Bieber has kicked off the first date of his world tour in dramatic fashion, after throwing up on stage.

Amateur footage uploaded onto YouTube shows the star vomiting twice in Phoenix on Saturday night.

He left the stage after each episode but returned and even did an encore, asking his screaming fans: "Will you love me even though I'm throwing up on stage?"

He tweeted afterwards: "Great show. Getting better for tomorrow's show !!!! Love u", before later revealing the cause of his mystery illness, adding: "And .... Milk was a bad choice!"