Britney Spears' residency is already the best-selling Las Vegas show of the year.

The "Perfume" singer, who kicked off Britney: Piece Of Me at Planet Hollywood Resort and Casino on December 27 last year, has already outsold Las Vegas residencies by Celine Dion, Elton John, Shania Twain and Rod Stewart. It is also the third highest-selling residency ever, behind Elton John's, which began in 2009, and Celine Dion's show, which started in 2011.

The 32-year-old star has only performed four shows so far, but tickets are on sale for concerts through to September. According to ticket website StubHub, 14 per cent of all tickets sold for Britney's show so far this year were for her February 14 concert, although they have declined to provide exact sales figures.

A number of big names have already been to see Britney live in Las Vegas, including Katy Perry, Adam Lambert and Miley Cyrus, who was seen dancing on the front row during the first 90-minute show in December.