There were no reports of any fatalities from the incident which broadcaster Radio Galega said left 266 people injured at the O Marisquino festival in Vigo, a town in the Galicia region.
Vigo’s mayor Abel Caballero said the platform that collapsed just before midnight was 30 meters long and 10 meters wide.
“There were loads, I mean loads of people” on the boardwalk, one witness told RTVE.