A tower of rocks suddenly broke away from the canyon wall and came crashing down on several leisure boats, sending out a huge wave over the lake at Capitolio, in Minas Gerais state.
The horrifying moment the canyon cracks[/caption]
It then falls on to the tourist boats[/caption]
Three boats were sunk after being struck[/caption]
Video images showed a gathering of small boats moving slowly near the sheer rock cliff on Furnas Lake when a fissure appeared in the rock and a huge piece toppled directly onto at least two of the vessels.
At least one wrecked boat sank, others sped away.
Firemen, including divers, said they were searching for 20 people believed to be missing.
The people hurt in the accident had broken bones and one was in serious condition in hospital with head and facial injuries.
Some 23 others were treated for light injuries, fire department spokesman Pedro Aihara told reporters.
According to Globo.com, passengers in other boats had noticed the canyon cracking.
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They then reportedly desperately called out to warn the other craft.
Lake Furnas is a popular tourist spot with natural canyons and navigable waters plus nearby hotels and holiday homes.
Minas Gerais state Governor Romeu Zema tweeted: “Today we are suffering the pain of a tragedy in our state, due to heavy rains, which caused the loosening of a wall of stones in Lake Furnas, in Capitólio.
“The Government of Minas is present from the beginning through the Civil Defense and Fire Department.
“Rescue work is still ongoing.
“I stand in solidarity with families at this difficult time. We will continue to act to provide the necessary support.”
The Brazilian navy has launched an investigation.
Passengers in other boats reportedly had noticed the canyon cracking and called out to warn the other pleasure crafts[/caption]