NEW YORKBritney Spears kicked off her 27th birthday Tuesday (December 2) not just with the release of her Circus album, but with a performance on "Good Morning America." Fans lined up in Times Square, where the mini concert was held, hoping for the opportunity to catch a glimpse of Britney in person.

The performance found Britney decked out in her Circus gear: midriff-baring shirt, a ringmaster jacket and top hat, and she alternated between hot pants and a pair of body-hugging leather pants. Brit and a group of dancers, jugglers and performers dressed as circus animals performed two songs from the album: the title track and "Womanizer," which also were featured in the singer's documentary, "For the Record," which premiered on MTV Sunday night and is re-airing throughout the week.

Spears also announced her world tour dates, which will begin in her home state of Louisiana on March 3, 2009. The Pussycat Dolls will be the supporting act.

Fans were cheering so loudly that Britney said she couldn't hear a thing. "That's so sweet," she said. "Thank you!" During the show, celebrities including Hugh Jackman, Reese Witherspoon, John Travolta and Taylor Swift sent the pop star birthday wishes, and "GMA" hosts Robin Roberts and Diane Sawyer presented her with a birthday cake.

Also in attendance were Britney's young sons, Jayden James and Sean Preston, and her mom, Lynne.

"They were cheering her on, they were excited! They were so cute," said fan Emily Rehm, who, along with friend Giffy Rahini, was seated two rows behind Britney's family at the performance. "[Britney's set] was so amazing. It was awesome."

"It was incredible, better than what I expected," said Dayna Caerafice, who was with her friend Jessica Mullen. "It was hot. It was amazing."

"[She looked] better than she's ever looked before," the friends said. "She just looked amazing." The duo, who got there at 6 a.m., even made special T-shirts to show their support for Britney, although they were less than pleased with the results. "Well, my printer was having a mishap," Mullen joked, displaying the shirt. "This was her face, but it's not anymore."

Three other fans, who traveled from Maryland and Washington, D.C., to attend Spears' big "GMA" performance, told MTV News that the experience was well worth the effort. "It was great. It was my first time ever seeing her live," said Jamal Jolly, who was with friends Anthony Johnson Jr. and William Jefferson. "Britney's back!"

(Tell us what you thought of Britney's documentary over on the Newsroom blog, or upload a video to YouRHere.MTV.com. "Britney: For the Record" will be re-airing throughout the week and will be available in its entirety on demand on MTV.com beginning Wednesday at 8 p.m. ET.)