Pop star Demi Lovato recently traded in the microphone for the steering wheel to go undercover as a cab driver in Denver, Colorado.

The Skyscraper hitmaker signed up to surprise fans as part of a funny promotional video series for car service Lyft, and hopped into the driver's seat ahead of her early August (16) gig in Denver as part of her joint Future Now Tour with Nick Jonas.

During her stint as a Lyft driver, Demi picked up unsuspecting passengers and introduced herself as "Samantha", telling them she was an aspiring singer who was desperately trying to break into the music industry.

"I actually really want to be a singer someday," Lovato told one female passenger. "Like, I've actually been travelling the country with my ex-boyfriend's brother because he sings, too. And so we really want to kind of get our names out there at open mic nights and, like, whatever we can do."

Demi even showed off her vocals by joining her passenger in belting out a tune from her Disney movie Camp Rock, in which she starred with the Jonas Brothers, and Happy Birthday.

The funny video, published on People.com, also features the singer, as Samantha, poking fun at Demi's musical talent, after one woman compliments a recent single.

"I like that Confident song. That's a jam," she commented, prompting Lovato to reply, "I like that one, but it like, sounds like she's screaming. Selena (Gomez) is so much more talented. She's got such a better voice (sic)."

At the end of each ride, Demi took off her sunglasses to reveal her true identity, leaving her passengers in awe.

After the surprise, one girl remarked of the ride, "It was super, super, super weird. She said she was a singer and she was touring with her ex-boyfriend's (brother)... That makes sense now. OK!"

Demi briefly dated Nick's brother Joe Jonas in 2010.

Taking to Twitter on Wednesday (31Aug16) after the video was made public, Demi wrote, "Had way too much fun surprising some @lyft passengers on my day off from #CastOnTour & Future Now #UndercoverLyft".

Other stars to take part in the promo campaign include basketball great Shaquille O'Neal, retired American football star Jerry Rice, and racecar driver Danica Patrick.