More than 300 people were injured Sunday night after an oceanside boardwalk in Spain collapsed during a nighttime concert.

According to The Associated Press, a three-day festival was coming to a close around midnight Sunday in the popular tourist town of Vigo when the boardwalk began coming apart, sending concertgoers into the water below.

Galician region health authority Jesus Vazquez Almuina said 313 people required medical treatment, with five of the victims listed as seriously injured, but no life-threatening injuries reported.

Vigo port authority president Enrique Cesar Lopez Veiga told the media that officials believe a structural problem in the boardwalk caused the collapse, likely brought on by the excessive weight of the concertgoers.

As a result of the accident, Vigo mayor Abel Caballero has launched a formal investigation.