Blake Shelton and Gwen Stefani surprised concertgoers in Las Vegas by putting on an impromptu show over the weekend.

The couple attended the Academy of Country Music Awards together on Sunday and following the prizegiving Shelton announced on Twitter he was hosting a free concert at the House of Blues with "friends".

He ended up taking to the stage with his fellow The Voice coach Kelly Clarkson and his girlfriend, who performed her hit songs, including Hollaback Girl and Hella Good.

"So, I know it's weird that I'm up here…, but we all have one thing in common and it's that we love Blake Shelton very much," Stefani told the crowd.

Gwen's surprise performance comes a week after the singer announced she will be staging a 25-date Las Vegas residency, dubbed Gwen Stefani – Just a Girl, at the Zappos Theater inside Planet Hollywood Resort & Casino.

"To be able to do a show in Vegas is such an incredible honor," a statement read. "Growing up in Anaheim, California, I could never have imagined one day having my own Vegas residency. I have been so fortunate to tour throughout my career, but to create a show for Vegas is something I've never experienced and I can't wait."

The residency kicks off on 27 June and runs into July before resuming in December, when she will perform four dates including one on New Year's Eve. The final run will start at the end of February and conclude in March.

Gwen and Shelton have also teamed up with officials at Live Nation in Las Vegas and Caesars Entertainment and the Cure 4 The Kids Foundation, which provides medical treatment to children with life-threatening conditions, and will donate $1 from every ticket purchased to the organization.