Miley Cyrus partied it up when she attended Britney Spears' Britney: Piece of Me show at Planet Hollywood in Las Vegas on Friday, Dec. 27.

A video caught Cyrus dancing and singing along as Spears performed Till The World Ends. In another clip, the 21-year-old danced with Spears' backup performers and even appeared to kiss one.

Spears, who just kicked off her two-year Vegas residency, expressed her gratitude for Cyrus' appearance and tweeted, "@MileyCyrus Love you so much! Thank you for coming to #PieceOfMe! I adore you :)."

Cyrus, however, wasn't the only star in the building. Selena Gomez and Katy Perry also attended Spears' first 90-minute Las Vegas show.

"Soy excited to see @britneyspears baby bottle pop it off tonight at her grand opening @phvegas! We are coming in full lewks to support!" Perry tweeted before the event.

Watch Cyrus dance front row at Spears' concert.

To that, Spears replied, "@KatyPerry Was SOOOO good to see you again girl! Glad we could make our Vegas date happen :)"

Aside from the celebrity attendees, Spears' show also received some rave reviews from critics.

"Spears stomped into town with a 21-hit salute to her 15 years of dance confections the artfully melded spectacle with stagecraft," USA Today writer Marco della Cava wrote in his Saturday review.

MTV News writer Sophie Schillaci said: "Spears delivered on her signature style of larger-than-life production, blaring beats and rapid-fire dance moves, whirling through seven costume changes and even a couple of wig changes."

Tags: Britney Spears Miley Cyrus