A young girl collapsed on stage during Katy Perry's tour stop in Detroit.

The incident occurred around 10.20pm at Little Caesar's Arena when Perry invited three fans to join her on stage to play maracas during one of her songs.

Perry paused the Sunday show, offered a prayer, and later reassured the audience the fan was doing better.

Eyewitness Alexandria Cross, 34, a pharmacy technician from Flushing, Michigan, said Perry made the unusual choice to select a fan from the furthest section of the venue.

"She turned out the lights in the stadium. She saw her blue skirt and pointed her out from way at the top, very back row," Cross said."

"I've never seen anybody get chosen that far back."

The pop star paused her performance while waiting for the girl to make her way down from the nosebleed section.

"She waited the whole time that the kid came down; the kid had to take an elevator," Cross added"

"She did not think that she was ever going to get chosen."

When the young fan finally reached the stage, accompanied by a friend, the crowd erupted in cheers.

But Cross said the girl appeared visibly nervous.

"She was very shy," Cross added. "She was very, very timid, and she got on the stage. "

"She obviously was super excited, but very stiff."

Perry attempted to reassure the overwhelmed fan.

"Katy wanted her to stand right next to her and gave her the shaker," Cross said. "

The situation took a dramatic turn moments later when Perry gave the girl a final pep talk before the song began.

"She's like, 'you got this.' Giving her kind of a pep talk," Cross added"

"And right at that moment, the girl just fainted. She just dropped right then and there."

Band members initially tried to assist.

"Eventually, the EMS ended up coming on there. There were six people or so that were all around her, trying to get her to wake up," Cross said. "

"They couldn't get her to wake up. So four or five of them kind of lifted her up."

The girl's mother, who had made her way down from the upper section, joined them on stage and followed as the unconscious fan was carried off.

"Katy did a prayer for the kid, and then she did the song," Cross said."

The singer later provided an update to concerned fans during another segment of her performance.

"She gave us an update that she's doing a lot better," Cross said. "She was very concerned about her throughout, which was super sweet."