Singer Justin Bieber has appeared in a controversial video in which he is seen telling a racist joke.

Contactmusic.com reports that the video clip, posted online by the The Sun newspaper, shows him joking with friends and uses the 'N word' five times after asking them: "Why are black people afraid of chainsaws?"

One friend repeatedly warns the pop star: "Don't even say it. Don't say it," but he laughs and says: "Run n****r, n****r, n****r, n****r, n***r."

The 20-year-old seems to have been 17 when the moment was captured on camera during filming for his first documentary "Never Say Never" in 2011.

According to The Sun newspaper, Bieber and his management have known about the video for a while and tried to pay for it to be kept out of the public eye.

"This video is Justin Bieber and his camp's worst nightmare. Even after the year he's had - when he's never been far from controversy - this tops it," said a source.

"He's made millions from working with musicians from all ethnic backgrounds. Having this attributed to him will do him no favours in the future.

"This could be the end of the road for him if artists refuse to work with him based on this. And it sets a seriously bad example to his impressionable young fans," added the source.

Singer Usher had discovered the pop star.