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MADRID (AP) — A stage structure being set up for a music festival collapsed Friday in northwestern Spain, injuring four workers, regional emergency services said.

Spanish National Television said 20 people had been working on the main stage when the accident occurred outside the city of Santiago de Compostela shortly before midday.

The four workers were temporarily trapped under the metal structure. One was in serious condition.

The stage was being prepared for the O Son do Camiño festival next week.