Pop star Jessie J posted this picture on her Instagram account. (Instagram)

Pop star Jessie J has shaved her head for charity.

The singer showed off her new bald look during Friday night's Red Nose Day telethon as part of Britain's Comic Relief festivities.

The giddy star said, "It's the weirdest feeling... It feels so liberating."

The star has raised over $800,000 for the cause after offering to shave off her long dark hair, and admitted the drastic haircut and the money fans had paid to will her on had really stunned members of her family, who were backstage at the telethon.

She added, "Everyone's crying. My mum's back there, my mum's crying with happiness."

She also took to Twitter.com to thank fans who had donated charity cash, writing, "I did it! Thank you to everyone who is donating!"

The Red Nose Day telethon highlights also included a live performance of One Direction's 2013 Comic Relief anthem One Way Or Another (Teenage Kicks).

Harry Styles kicked off the song, wearing a comedy red nose, and bandmate Louis Tomlinson celebrated the big gig by dying his hair red.