"Queen of pop" Madonna entered the stage on a throne on Saturday as she kicked off her world tour, and defied her age with athletic dance routines before tens of thousands of screaming fans.

The U.S. singer, who turned 50 a week ago, opened her "Sticky & Sweet" tour at the Millennium Stadium in Cardiff, Wales. She wore a black leotard-style outfit designed by fashion house Givenchy and black, knee-length boots.

For her second number, "Beat Goes On," Madonna drove along the stage catwalk in a white car from which she emerged wearing a white top hat.

U.S. rappers Pharrell Williams and Kanye West, who featured on Madonna's latest chart-topping album "Hard Candy," appeared in video clips, as did Britney Spears.

Madonna will be hoping to shatter her own record for the highest-grossing tour ever by a female artist and prove that the musical master of reinvention still has what it takes to pull in crowds young and old.

"It was so charismatic," said Paul, from the Welsh city of Newport, after the show. "I don't believe she's 50. She's more like 30."

"I think she's amazing," added Morgan, a young girl from Cardiff. "I want to be that way when I turn 50."

During the show Madonna played around 20 songs which spanned a career of nearly three decades, including some of her biggest hits.

The concert moved from a homage to 1920s art deco to the early 1980s music scene in New York, the city where, according to online biographies, Madonna moved in 1977 to pursue a career in dance with just $35 in her pocket.

Promoters Live Nation, who recently signed Madonna to a 10-year deal reported to be worth $120 million, said Madonna and her band clocked up 653 hours of rehearsal time before launching "Sticky & Sweet."

The tour comprises some 50 dates and is due to wrap up in Sao Paulo, Brazil, on December 18.

As of Thursday, roughly half the tour venues had yet to sell out including Cardiff, although Live Nation announced in June that the tour was on target to gross more than $250 million.

Guinness World Records list Madonna as the world's most successful female recording artist of all time and she has sold around 200 million albums. The Sunday Times estimates Madonna and husband Guy Ritchie's fortune at around $600 million.

But the last few years have not all been easy for Madonna.

Her decision in 2006 to adopt a young Malawian boy whose mother died was controversial in Africa and further afield.

Madonna has two other children -- son Rocco with British film director Ritchie and daughter Lourdes from a previous relationship. The family was in Cardiff to watch the show.

She directed her first feature film that came out in 2008 to mixed reviews, and her eight-year marriage to Ritchie has come under increasing scrutiny amid reports the couple planned to divorce. Both Ritchie and Madonna have denied the reports.

Source : Reuters