They were built in the Muzema favela on Rio’s western outskirts, which was devastated by days of torrential rains and catastrophic flooding.
Rio municipal authorities said they wanted to tear down three surrounding buildings and invite engineers to assess several others to prevent further collapses.
The rescue operation continues with the help of a hundred military personnel, sniffer dogs, drones and helicopters, the public news agency Brasil said.
Favelas in Rio are usually run by shadowy militias that use violence to enforce their rule. They sell land rights and also control access to water and electricity. Many buildings in the favelas are poorly constructed and have no permission from city planning authorities.