A massive rock formation fell on top of three boats in the Brazilian state of Minas Gerais on Saturday morning, leaving at least five people dead and about 20 injured, officials said.

       Video shows the rock slab break away from a canyon wall while onlookers scream. The collapse caused a massive wave that sent boats flying, a clip shows, with at least one wrecked boat sinking into the water. Brazilian authorities verified the authenticity of the video.

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       Officials were searching for 20 people believed to be missing, Pedro Aiharas, a spokesperson for the Minas Gerais Fire Department told The Washington Post. He said that about 20 people were treated at the scene, and that nine were taken to hospitals with serious injuries. One person was in critical condition with head and facial injuries, and at least five people were killed.

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       According to the fire department, it was unclear how many vessels were affected by the rockslide. Authorities believe the accident sank some of the boats closest to the rocky walls around Lago de Furnas.

       What triggered the rock’s collapse remains unknown.

       Rovilson Teixeira, who has worked with a speedboat transport company for six years, told Brazilian outlet O Tempo that he had never seen anything like it happen in the region.

       “We are all stunned; nobody knows how many victims, but I can already tell you that there were not one or two deaths, but many deaths,” Teixeira said. “There are a lot of hurt people. The region is full of ambulances that have come from other areas to pick up the victims, but no one yet realizes the scale of the tragedy here.”

       This is a developing story that will be updated.