The incident happened on Sunday during a concern as part of O Marisquino three-day culture and sports event in Vigo. According to the local authorities, seven of those injured remained in hospital.
According to Vigo's mayor Abel Caballero, the platform collapsed just before midnight and was 30 metres long and 10 metres wide. Caballero said local and national police and civil guard were active on the scene.
People attending the concert said the crowd was enjoying the concert when they heard the broadwalk breaking.