Four days after the disaster struck a poor hillside neighborhood, rescuers are working around the clock searching for survivors in the rubble with the help of sniffer dogs.
Another 10 people were injured when the adjacent buildings in Muzema favela buckled, days after torrential rain wreaked havoc in the city.
Many of the cheaply made apartment towers in Muzema were erected without permission from city planning authorities.
Like many poor neighborhoods in Rio de Janeiro, Muzema is run by shadowy militias that use violence to enforce their rule.
They sell land rights and control access to city services such as water and electricity.
Authorities have pledged to demolish some of the surrounding buildings in Muzema to prevent further collapses.
But residents complained that Muzema and surrounding areas had long been neglected by the Rio de Janeiro government.
As soon as illegal buildings were demolished, new ones were built in their place, they said.