Britney performing on Good Morning America

Britney Spears celebrated her 27th birthday under the Big Top and before the TV cameras of Good Morning America.

Dressed as a ringmaster, Spears made her entrance atop a circus wagon – accompanied by clowns, jugglers and performers dressed as circus animals. For her second number, "Womanizer," Spears smashed through a fiery hoop.

Afterwards, she announced that her concert tour would begin in New Orleans March 3. Then came the cake.

The appearance, inside the Big Apple Circus tent within New York's Lincoln Center, also marked the launch of Spears's sixth studio album, Circus – her first CD since her 2007 comeback step, Blackout.

Mother and Sons Attend

As Spears announces on the title track (and delivered on GMA), "There are only two types of people in the world, the ones that entertain and the ones that observe." GMA's Robin Roberts called Spears's appearance "our concert event of the year."

Claimed cohost Diane Sawyer about those gathered inside the circus tent, "There are about a gazillion people [here]."

Among them: the pop star's mother, Lynne Spears, and Britney's two young sons, Preston and Jayden.

Interspersed with the promos for Spears's performance during Tuesday's GMA were birthday greetings from the likes of Reese Witherspoon, John Travolta, Nicollette Sheridan, Teri Hatcher and PEOPLE's newly named Sexiest Man Alive, Hugh Jackman – who sang "Happy Birthday" and blew her a kiss.

"You look great," Witherspoon relayed to Spears, "and I hope you have a great day." Added Taylor Swift: "You have been officially awesome for 27 years."

Source: People.com