Britney Spears has admitted to having numerous panic attacks on her first day as an X Factor USA judge.

The singer signed up to appear on the TV talent show earlier this year at the same time as fellow newbie Demi Lovato.

Speaking to Elle magazine, Spears said that she was fraught with nerves, however, when it came to filming the series. She said:

"I was having panic attack after panic attack."

Spears also admitted to feeling bad over turning down fledgling wannabes, but she soon realised that she was "helping them".

X Factor supremo Simon Cowell meanwhile is quoted as saying that he initially thought the 'Circus' star wasn't going to be able to carry on - but he admitted he was quickly proved wrong. Cowell said:

"On the first day, one hundred percent she didn't think she was going to be able to do this. It's the Roman Colosseum - five thousand people booing if you say no. But I'm seeing this woman blossom week by week doing this. I think she's going to be good for the show, and I think the show is going to be good for her."