Dramatic videos show deadly cliff collapse in Brazil

At least seven people were killed and three were missing after a cliff collapsed onto boats carrying tourists on a lake in Brazil, authorities have said.

Rescue teams including a dive squad and members of the Brazilian Navy rushed to Furnas Lake in Minas Gerais state, where panicked tourists had watched helplessly as a large rock fragment broke off a ravine and plunged atop three boats.

The latest official toll is "seven dead and three missing," Minas Gerais firefighters' spokesman Pedro Aihara said.

Another 32 were wounded, including nine who had to be hospitalized. Firefighters had initially reported 20 missing, but "that number was substantially reduced because a good part of the victims who were unaccounted for were people who moved by their own means to hospitals," Aihara said.

Tourists flock to see the rock walls, caverns and waterfalls that surround the green waters of Lake Furnas, formed by the hydroelectric dam of the same name.

Dramatic videos shared on social networks catch the exact moment when the cliff fell on the three boats.

Another video shows the minute before the collapse, in which several people warn that "lots of stones are falling" and yell at the occupants of the other boats to move away from the wall.

President Jair Bolsonaro retweeted some of these videos on his account.

The divers' search was set to be interrupted overnight for safety reasons and resumed in the morning, but other rescuers continued to work at the site. Very heavy rain has fallen in recent days in southeastern Brazil, making the collapse more likely, according to firefighters.

Commenting on the collapse, adjunct associate professor Chau Kwai-cheong from Chinese University said cliff collapses are not uncommon as joints appear in rocks exposed to the atmosphere, which could then widen due to weathering, earthquakes and other geological activities.

"Those joints grow in size and reach a tipping point before gravity comes into play," Chau said.

There are also landslides and soil creeps on slopes in Hong Kong, but similar incidents are unlikely to happen in the SAR, Chau said.

He reminded people to avoid visiting cliffs after strong rain or wind as rocks will be saturated and more likely to collapse. They should keep their distance from cliffs, Chau added.