Adele was left visibly impressed by a Christian fan who spontaneously joined her on stage during her US tour and sang for her.

Grammy-nominated Jamie Grace was invited on stage by the Someone Like You singer at her concert at the Staples Centre, Los Angeles on Tuesday night.

"She was being super interactive with her fans...and then she looked at me and I said, 'Do you want to sing together?' And she said, 'Okay, come up here!' So I went up there," Grace told ABC News.

Grace, whose song Hold Me gained her a Grammy nomination for Best Contemporary Christian Song in 2012, posted footage from the night to her Instagram and Facebook accounts and the posts soon went viral.

On Grace's Facebook page alone the video has racked up more than 1.2 million views.

The 25-year-old chose to sing Adele's Remedy and then Elvis Presley's I Can't Help Falling in Love With You, which she referred to as her "parents' song" in an Instagram video of the performance.

To Adele's surprise, her fan's vocals were far from amateurish.

In the footage Adele can be seen placing her hands over her chest, raising them in the air and exclaiming as Grace sings acapella to the crowd.

At the end of Grace's impromptu performance, Adele embraces the 24-year-old singer as the crowd applauds.

The singer-songwriter, who hails from Atlanta, had told fans in a personal Facebook post the Saturday before the concert that she had considered retiring from music.

"I've legitimately contemplated retiring. 100% fact. Not too embarrassed to say I sought out a Christian counselor since last year. I've been trying to process why I feel like God is calling me to this amazing purpose yet for some reason things just aren't working out.

"There's an element of professionalism I've tried to maintain but the truth is I'm a human who has been broken and hurt and that remains. I am grateful for experiences I have had but if waking up every morning HOPING you get to share a new song is a part of 'living the dream'?" I want no part of it," she wrote on Facebook.

Commenting underneath the video of Grace on stage with Adele and referring to her comments about the direction of her career last week, one fan wrote: "You remember your post from last week about your career not moving forward? Um yeah, I think God is sending you a message."

Grace has since told ABC News: "It was a reminder and an assurance that I do have a voice and the voice does matter. It was everything I needed."