Images shared on social media showed the moment the structure buckled under the weight of dozens of supporters, sending some fans tumbling onto others standing below.

"Emergency under control: the five injured people were treated by personnel" from the emergency services, the fire brigade said on Twitter.

Around 20,000 fans had turned up to Colo Colo's Estadio Monumental David Arellano stadium in Santiago for the team's last training session ahead of Sunday's local derby against Universidad Catolica, the reigning champions.

"We've told them many times, in campaigns, in everything: everyone has to behave themselves," the club's Uruguayan midfielder Maximiliano Falcon said on the Colo Colo Twitter account.