Young people leave the Medusa music festival after high winds caused part of a stage to collapse, in Cullera, near Valencia, Spain, August 13, 2022.
The incident occurred shortly after 4:00 am (0200 GMT) at the Medusa Circus of Madness dance music festival on Cullera beach, some 50 kilometres (30 miles) south of Valencia.
"At 4:18 am, part of the stage at Medusa Festival collapsed in Cullera due to a strong gust of wind," the 112 emergency services said on Twitter.
"One person died and three were seriously hurt with multiple injuries," it said, indicating 14 others sustained light injuries. The health authorities later raised the toll to 40 injured.
Media reports said a young man in his early 20s died after being hit by parts of the stage as it collapsed at the event which had been expected to draw some 320,000 festivalgoers.
They also said some of the large structures making up the festival entrance also blew down.
Footage on social media showed powerful winds sweeping through the venue, trees and large structures bending dangerously, and debris flying everywhere as people fought to hold onto their tents and salvage their belongings.
Spain's AEMET weather service said the Valencian coast had been hit overnight by various "warm downbursts", a weather event in which a powerful downward current of air hits land then spreads out in all directions.
"We are completely devastated and appalled by what happened last night," the festival management said in a statement on social media, conveying condolences to the victims and their family and friends.
It said an "unexpected and violent gale" had ravaged certain areas of the festival just after 4:00 am, forcing the management "to immediately evacuate the concert area to ensure the safety of the festival goers, staff and artists".
Valencia's regional leader Ximo Puig wrote on Twitter it was "a terrible accident that has shocked us all", offering his "deepest condolences to the family and friends of the young man who died".