WENN

Sam Smith has been forced to cancel his latest set due to a "vocal emergency".

The British singer was scheduled to perform a 25-minute concert on Friday at the iHeartRadio Music Festival at the T-Mobile Arena in Las Vegas, when host Ryan Seacrest made the announcement.

"Due to unforeseen circumstances which transpired after his rehearsal, it became clear that Sam Smith would unfortunately not be able to perform tonight," he told the disappointed crowd, explaining that Sam had suffered "vocal emergency" on the day. "We love Sam. Sam has been part of our iHeart family for many, many years and we look forward to seeing him really soon."

The 26-year-old also shared a statement on Twitter, and wrote: "Dear all, Due to unforeseen circumstances which transpired after rehearsal, it became clear that I'm sadly unable to perform at the iHeart Radio Music Festival in Vegas tonight. I am so so sorry about this and I want to apologize to all my fans. All my love, always. Sam x."

A rep for the Stay with Me singer also told Variety that Sam was "extremely sorry".

According to editors at Billboard, Sam had complained his throat was hurting during rehearsals earlier on Friday, and then lost his voice.

The Oscar-winning star reportedly left Las Vegas on a chartered flight to Boston.

But Donald Glover, who performed under his stage name Childish Gambino, stepped up and started his set earlier to cover for Sam's absence.

The 34-year-old arrived at the venue in a wheelchair, but had recovered enough to deliver a rousing rendition of his track, Redbone.

Fleetwood Mac, Panic! at the Disco and Mariah Carey were among the rest of the evening's performers.