Hopes began to fade of finding any survivors in the three collapsed buildings in the Brazilian city of Rio de Janeiro as firefighters pulled out more bodies and the death toll rose to 17.

A Rio de Janeiro fire department official said the search for survivors would continue at least through Sunday, but the chances of finding anyone alive are "practically nonexistent."

The official, who declined to be named because he was not authorized to speak to the press, said rescuers pulled five more bodies from the debris overnight and early Saturday morning. The death toll had been 12. Seven people are still missing.

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It's not yet known why the 20-story building suddenly collapsed Wednesday night, but authorities say they suspect unauthorized construction work inside the large, 72-year-old building created structural damage that led to the fall.

Officials believe the falling building wrenched down two neighboring office buildings of approximately the same age.

The collapsed buildings in Rio's historic center contained of a wide range of businesses. Most tenants were gone by the time of the tragedy, but some had remained to finish leftover work. Several of the missing were in a computing course.

Rio's Regional Council of Engineering has said the last time they authorized refurbishing in the 20-story building was in 2008. But Mayor Eduardo Paes said a license from city hall is not required for internal construction projects, and the responsibility for such projects lies "exclusively in the hands of workers."

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The head of Rio state's Civil Defense agency said the hunt for survivors will continue for 48 hours more.

City officials said the accident should not cast doubt on Rio's ability to organize and host the upcoming Olympics and World Cup.

"This was an isolated incident that occurred on private property," the mayor's office said in a statement. "The case is entirely unrelated to the preparations for the 2014 World Cup, the 2016 Olympic Games and other events that are already part of the city's calendar."

Based on reporting by the Associated Press.

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