Ten were seriously injured with three in critical condition, police said, after two giant stages collapsed, whole trees were uprooted and hailstones “the size of golf balls” rained down on petrified youngsters, witnesses said.

Organisers, who had raised “sold out” signs for crowds of 65,000 fans on each of the three days the event was due to run, promptly called a halt to planned performances by global names such as Eminem and the Foo Fighters.

King Albert II and Queen Paola cut short their holidays, and were to pay tribute to the victims at the site on Friday evening — as a refugee-like exodus of muddied, confused teenagers traipsed away from the nightmare.

The storm “cost the lives of five people,” Hasselt mayor Hilde Claes said, adding that all five were Belgian citizens, and that in total, 140 people had received medical treatment. Two of those in critical condition were Dutch citizens.

Claes said initial checks on emergency planning measures, which staff told AFP included “checking trees for their resistance to high winds, and testing the drainage system,” left officials confident they had done everything that could be expected of them given such freak conditions.

Youngsters among the sorrow-stained figures beginning long journeys home after sleepless nights in rain-soaked tents said no blame could be attached to the authorities.

Up to 65,000 people, mainly young, were thought to have been present at the outdoor Pukkelpop festival — already the scene of a suicide tragedy last year — when the storm hit.

“I was under the party tent when it came crashing down, we had to run for our lives,” spiky-haired 17-year-old Matthias Vannievwenhuyze of western Flanders told AFP as smashed-up giant television screens and other debris still littered the site.

“Hailstones almost the size of golf balls were raining down on us, I saw one girl knocked flat out when they hit her on the head.

“People were panicking, and a few minutes later, I saw medics lift her on to a stretcher.

“When they put a blanket over her, I knew she was dead — I hate to admit it, but at that moment, you don’t think about other people’s losses, you only think about yourself.”

News of the chaos, which spread rapidly via mobile phone footage on social networking sites, brought thousands of parents from around Belgium and the Netherlands flooding into the site.

“People drove 200 kilometres (125 miles) to come and look for their children after watching the evening news,” festival crew member Christel De Vries told AFP as the clean-up operation got under way on Friday.

“Parents were walking up and down the road at the main entrance shouting out the names of their children — the anguish on their faces was so emotional for me as a parent myself.”

Neighbouring home-owners and youths told AFP how doors were thrown wide open throughout the night, with phone access, hot drinks and clean showers offered to confused strangers.

After ambulances rushed to the scene as the concert came to a halt, a crisis centre was set up in a gymnasium in nearby Kiewit suburb to help those who have been lightly injured or in shock.

Belgian Prime Minister Yves Leterme issued a statement offering his condolences to the families of the victims, and Brussels-based European Commission president Jose Manuel Barroso also extended the EU’s condolences.

Last year, two tragedies occurred: a sound engineer died of a heart attack, and a rock singer, Charles Haddon, committed suicide by jumping from the top of a pylon after his group performed.

Last week in the United States, an eerily similar tragedy occurred at the Indiana State Fair, ferocious winds bringing down rigging and killing five and injuring 45 others.