LONDON: Britney Spears has sung live for the first time on her 'Circus' world tour, performing a cover of Alanis Morissette's 'You Outta Know'.

Britney Spears has sung live for the first time on her 'Circus' tour.

The US star debuted a cover version of Alanis Morissette's 'You Outta Know' at a concert in North Carolina, US, last night (05.09.09) - the first time she has sung a song live on the worldwide tour since it began in March.

A concertgoer revealed: "We were really surprised! Nobody knew she going to sing that song. When I saw her rise up with a microphone I was thinking, 'what is she doing?' I had to ask the person in front of me what song she was singing!"

In a video posted of Britney performing the song, she sounds confident and strong as a singer again and after she finishes, the shocked crowd give out huge cheers.

Posting a text response to the video, one fan wrote: "This song is soooo good and seems so nice in Britney!

"Congrats Britney, you should sing more live. Even if it's not perfect it would be more exciting and emotional for you, and for the fans. [sic]"

Previously on the tour, Britney has mimed while concentrating on the complicated dance routines involved in the show.