The singer, who turned 21 on March 1, celebrated his milestone birthday with a group of A-list friends at OMNIA Nightclub at Caesars Palace in Las Vegas, flying to the party city after taping his episode of Comedy Central Roast.

Bieber was joined by Kris Jenner and her boyfriend, Corey Gamble, as well as Smash star Katharine McPhee, and his manager and mentor, Scooter Braun, at the party, which featured a birthday cake in the shape of a 1965 Lincoln Continental.

Although he has become known for his out-of-control antics while partying, Bieber seems to have had a relatively tame night. The singer spent some time in the DJ booth, enjoying the party.

"He was in great spirits," a source told E! News. "He was having a great time with his friends . . . He looked good."

Just a few hours earlier, the singer had been the centre of a different kind of attention, listening to celebrities and comedians make fun of him on the Comedy Central Roast set.

The jokes he was subjected to ranged from digs about his homeland ("Justin's Canadian. [But] he's actually considered American because no Canadian's ever been this much of an asshole.") to gags about his musical ability ("It seems like only yesterday you were discovered on the YouTube. Time flies when you're a piece of s---.").

However, the episode, which will air on March 30, seemed to focus attention on the singer's ex, former Disney star Selena Gomez.

Comedian Jeffrey Ross gave Gomez, who declined an invitation to attend the taping, a particularly hard time.

"Selena Gomez wanted to be here, but she's dating men now," Us Weekly reported the comedian as saying. "Is it true you dumped her because she grew a moustache before you?"

The most controversial of Ross' comments about Gomez came when he drew attention to the Heart Wants What It Wants singer's Mexican heritage.

"Selena Gomez had sex with [you] . . . proving Mexicans will do the disgusting jobs Americans just won't do," he said.

Gomez, 22, is yet to respond.

Comedy Central Roast is a television special in which celebrities are sledged by a mix of fellow celebrities and comedians. Previous "roastees" include Charlie Sheen, Roseanne Barr and James Franco.

Bieber had requested an appearance on the show.

"For years I have wanted Comedy Central to roast me," he tweeted in January.

"They said only if I provided them w/ more material so for a year now I have worked hard."

For years I have wanted Comedy Central to roast me. They said only if I provided them w/ more material so for a year now I have worked hard – Justin Bieber (@justinbieber) January 20, 2015