The crowd sang along to hits including Happier Than Ever after the 21-year-old told her 110 million Instagram followers she was "really suffering" ahead of her headline performance at the Irish festival on Friday.

Videos posted on social media showed her delivering her Barbie soundtrack song What Was I Made For? in a white Nike shirt and baseball cap.

Eilish had previously asked her fans to help her at the concert.

"I am really, really sick, and honestly really suffering," she wrote on her Instagram story.

"You know me and you know that I wouldn't cancel a show even if I was like literally dying… (this does feel pretty close tho lol) but the show must go on.

"I will see you tonight! But please keep in mind that I am trying my best and I'm gonna need your help tonight. Go hard for me."

Meanwhile former One Direction star Niall Horan, who sang Sinead O'Connor's hit Nothing Compares 2 U in tribute to the late singer, referenced his local roots in an emotional speech at the festival.

The Westmeath-born singer told the crowd: "I wish I could put into words how this felt. From Patrick Street, Mullingar, to this.

"This is a country with less than five million people, and the noise that we make worldwide is insane, and as long as you would like me to, I'm happy to fly the flag for our little country all over the planet.

"I love our little country. I love being here tonight. I love you all. Thank you so much for coming out to see me.

"This is by far the biggest audience I've played to as a solo artist and I really appreciate it, the support from my home nation.

"It's great to be back in the Midlands, only an hour away from home, and have this. Thank you all so much."