At least six people died when a huge piece of rock broke from a cliff and fell on to pleasure boaters drifting near a waterfall on a Brazilian lake on Saturday, officials said.
They said at least 32 were injured, though most had been released from hospitals by Saturday evening.
As many as 20 people might be missing and officials were seeking to identify them, said Edgard Estevo, commander of the Minas Gerais State Fire Department.
Video footage 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 on to at least two of the vessels.
Mr Estevo said the accident occurred between the towns of San Jose da Barra and Capitolio, from which the boats had left.
The press office of Minas Gerais state told the Associated Press that the fire department had sent divers and helicopters to help. Minas Gerais governor Romeu Zema sent messages of solidarity with the victims via social media.
Furnas Lake, which was created in 1958 for the installation of a hydroelectric plant, is a popular tourist attraction in the area roughly 420 kilometres north of Sao Paulo. Officials in Capitolio, which has about 8,400 residents, say the town can receive around 5,000 visitors on a weekend, and up to 30,000 on holidays.
Officials suggested the wall coming loose could have been related to heavy rains recently that caused flooding in the state and forced almost 17,000 people out of their homes.
Earlier last year, the concern was a lack of rain as Brazil experienced the worst drought in 91 years, which forced officials to divert the water flow from the Furnas Lake dam.
The Brazilian navy, which also helped in the rescue, said it would investigate the causes of the accident.