After Saida Maria Prieto, 25 -- wearing a winged and feathered "Isis, Queen of the Gods" costume -- finished seventh in the contest, a fire believed to have been started by fireworks, struck the backstage area of the event venue, the website ThinkSpain said.
"The scene was horrific, terrifying," a TV reporter said. "A curtain caught fire and in less than a second, flames of 10 meters [32 feet] in height reached the ceiling."
Prieto suffered burns to 40 percent of her body and was transferred to the burn unit of Virgen del Rocio hospital in Seville, Spain, where she was reported in serious condition.
Four other people were treated at the scene by the Red Cross for first-degree burns, ThinkSpain reported.
Swim Week Miami Beach 2014 [PHOTOS]