LAS VEGAS (AFP) - Pop superstar Taylor Swift offered a new personal transformation on Sunday as she debuted a video of herself as an feminist action hero in collaboration with rapper Kendrick Lamar.

Opening the Billboard Music Awards, she premiered Bad Blood as the fourth single from her album 1989, which was by far the top-selling solo album last year.

The single features Lamar, one of the most acclaimed rappers of the moment, in a hip-hop duet - a once unthinkable step for Swift, 25, who started off in country music before shifting to pop.

The song - whose chorus runs, "Baby, now we've got bad blood / You know it used to be mad love" - is about Swift's feud with another pop star, widely speculated to be Katy Perry.

But the video, directed by veteran music director Joseph Kahn, turns Bad Blood into a mini-action film, with Swift leaping into an office and dueling with baddies.

Hoping for a theme of women's empowerment, Swift enlists as her co-heroines a number of female stars ranging from model Cindy Crawford to actresses Zendaya and Selena Gomez to Lena Dunham, the creator of the dark television comedy series Girls. "Let the lethal forces of femininity rock you to sleep," Dunham wrote on Twitter ahead of the video's debut.

Swift in the video turns into a boxer and, with her hair momentarily dyed deep red, struts with a row of weapon-toting women.

After premiering the video, she opened the televised awards in Las Vegas by introducing rock veterans Van Halen, who performed their hard-charging 1984 hit Panama. She later accepted an award and embraced Scottish DJ Calvin Harris, who was sitting beside her, in images certain to reinforce gossip that the two are dating.

The Billboard Music Awards, run by the music trade magazine, recognise chart performance unlike the more prestigious Grammys which are based on voting within the industry.

Sam Smith, the British soul singer who was the big winner at the latest Grammys, missed the Billboard Awards as he underwent surgery on Thursday to repair a vocal cord problem.

Smith, who has cancelled weeks of shows, accepted a Billboard Award for top male artist through a video message. He silently held handwritten signs that included: "Can't wait to get this surgery out of the way so I can sing my ass off for you again."

The British boy band One Direction won for best duo or group less than two months after Zayn Malik departed.

"There's one more person to share this with, and that's our brother Zayn," Liam Payne said as he took the stage with his three fellow remaining bandmates.

The gracious display came after open acrimony between Malik and his former bandmate Louis Tomlinson.

Tomlinson had criticised Malik's producer Naughty Boy after Malik released solo work soon after the split. Malik then quipped over Twitter to Tomlinson: "Remember when you had a life and stopped making bitchy comments about mine?"