A slab of rock broke off from a cliff and fell onto boaters at a lake in southeastern Brazil, killing at least eight, authorities said on Saturday.

Two people are missing. Officials said at least 32 people had been injured but most had been released from hospital by Saturday evening.

A number of people had broken bones and one person was in serious condition with head and facial injuries. 

Firefighters had initially reported 20 missing, but this was later revised as many of those unaccounted for had made their own way to hospitals.

Video images showed a group of small boats drifting near a waterfall below a cliff on Furnas Lake when a piece of rock broke off, hitting at least two of the vessels.

Another video on social media shows the minute before the incident, with people warning that "many stones are falling" and advising other boats to move away from the rocks.

Where did the accident occur?

Authorities said the incident occurred between the towns of Sao Jose da Barra and Capitolio, located in Brazil's southeastern Minas Gerais state. The boats had left from the town of Capitolio.

Furnas Lake was originally formed along with the creation of a hydroelectric dam and is a major tourist attraction in the area.

Tourists come to see the rock walls, caverns and waterfalls surrounding Furnas Lake.

Why did the accident happen?

Officials suggested the rock could have come loose due to recent heavy rains that caused flooding in the state and displaced 17,000 people.

Pedro Aihara, spokesperson for the Minas Gerais State Fire Department, told Brazilian broadcaster GloboNews that the rocks in this area are "more susceptible to the effects of wind and rain" and "show less resistance."

sdi/nm (AP, AFP, Reuters, Lusa)