Critics cheer Spears' spectacle

Spears spoke to the crowd only once during the concert

US critics warmly reviewed the first night of Britney Spears' Circus tour despite suggesting that she was lip-synching some songs.

The performer started her world tour in New Orleans and revealed a 17 song set with dozens of costume changes.

Reviewers praised the energy of the spectacle, although several noted the singer mimed to a backing track.

The singer will perform in 31 North American cities before coming to the UK in June for eight shows in London.

The tour is supposed to seal Spears' professional comeback after a turbulent time for the singer personally.

With a lot riding on the opening night, Jim Farber of the New York Daily News said: "Spears dutifully hit her marks, kept up a robust pace and looked determined and engaged."

But celebrity blogger Perez Hilton complained: "She lipsynchs during the entire concert. There is no live singing."

Backing track

Ann Power of the Los Angeles Times said that despite her decision to perform to a backing track, the circus theme was apt.

A huge troupe of backing dancers performed circus acts

"Anyone who thinks her lacklustre would do well to remember what she really is: a burlesque performer," she wrote.

Jerry Shriver from USA Today added: "Amid the spectacle, it's impossible to tell how much of the singing is real, but the crowd couldn't have cared."

Fan Natasha Stcyr told Reuters: "The theatrics, the performance, it was great. Phenomenal. It was definitely a circus. It was awesome. She's definitely back."

But another concert-goer, Stephanie Chandler, told the news agency she was "very disappointed".

"She's just not in it. If you're going to lip-sync, then you'd better bring on the dancing, but she didn't," she told Reuters.

Spears has had an eventful personal life since her Onyx Hotel tour in 2004.

She got married and divorced, had two children, was admitted to hospital with mental health problems and been at the centre of court proceedings against a former manager and an ex-boyfriend.

Her father, Jamie Spears, is currently in legal charge of all of her affairs.

The tour supports the release of her Circus album, which has sold more than 1.3 million copies worldwide since being launched in December.