GLASTONBURY, United Kingdom  – Prince Charles charmed revellers at Britain's Glastonbury festival on Thursday, as they gear up for a weekend of top acts at the world's largest open-air festival.

He was surrounded by music-lovers as he arrived on the second day of the event in southwest England, this year celebrating its 40th anniversary.

"He asked me how the food was. This is amazing, I wasn't expecting to see him today," said Jack Rogers, 27, from London, while others shouted "We love you, Charles" as the prince made his way round the field.

Glastonbury founder Michael Eavis, dressed in a striped shirt and chinos, said it was a typical Glastonbury welcome. "They're a classless society," he said. "The prince seems to be really enjoying his visit."

Over 170,000 people are expected to attend the festival, which is renowned for attracting the planet's most revered musicians as well as encouraging more left-field and underground performance artists.

Organiser Eavis, 74, received a blow when Irish rock megastars U2, who were due to headline the main Pyramid Stage on Friday, pulled out after frontman Bono injured his back.

Stepping into the breach are Gorillaz, the hip-hop influenced side-project of Blur singer Damon Albarn.

Other heavyweights performing this year are US soul pioneer Stevie Wonder, rapper Snoop Dogg, Latino superstar Shakira, American quartet Vampire Weekend, country icon Willie Nelson and rockers Muse, who headline on Saturday.