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Rescuers retrieve the corpse of one of the victims of the collapse on the eve of three buildings in downtown Rio de Janeiro, Brazil, on January 26, 2012. Rescue teams frantically dug through rubble Thursday for 16 people missing after three office buildings collapsed in the historic heart of Rio, killing at least five people and injuring six, officials said. Image Credit: AFP

Rio de Janeiro: There is no hope of finding survivors from the three high-rise buildings that collapsed in central Rio, authorities said Friday, with the official toll at 15 dead and 12 missing.

Two days after the office buildings - of 20, 10, and four stories - crashed down near the municipal theater on the city's Cinelandia square, officials said 15 bodies had been recovered so far, 11 of them on Friday.

"Regrettably I must say that we no longer expect to find survivors," Sergio Simoes, the state secretary for Civil Defense, said Friday, noting that all the bodies extricated from the rubble so far "were badly crushed".

Many of the missing were believed to be in a classroom on the sixth floor of the 20-story Liberdade building where a computer firm was giving a training course when the structure collapsed.

"We expect to find a significant number of people there," Simoes said.

Late Thursday, Rio de Janeiro Mayor Eduardo Paes put the official toll at four dead, with 22 missing. A dense cloud of smoke still hung over the rubble from a fire that was still burning, beyond the reach of firefighters.

Suffering

The search was expected to end by Saturday morning "to minimize the suffering of families," of the victims, said Colonel Ronaldo Alcantara of the city's fire department.

Nearly 400 people are taking part in the rescue effort, including a contingent that was sent to Haiti during the devastating earthquake there two years ago.

The disaster could have been far more deadly if it had happened during the day, and it raised fresh questions about Brazil's preparations to host the 2014 Football World Cup and 2016 Summer Olympic Games.

The three buildings collapsed almost simultaneously for as yet unknown reasons, though authorities said they did not believe an explosion had occurred, as witnesses initially reported.

Structural problem

Investigators were focusing on a structural problem as the likely cause. Witnesses reported that remodeling work had been taking place on two floors of one of the buildings.

The work had not been cleared with the Rio Engineering Regional Council (CREA) and was therefore illegal, according to CREA official Luis Antonio Consenza. Police and the CREA have launched an investigation.

Brazil has had several calamities in recent months, including explosions caused by gas leaks, and fatal accidents in poorly maintained amusement parks or in packed streetcars with faulty brakes.

World Cup

City authorities are scrambling to upgrade the country's infrastructure and to build or renovate 12 stadiums around the country in time for the World Cup, one of the world's premier sporting events.

Last month football's ruling body FIFA warned Brazil about delays in the progress of construction projects expected to be ready for the four-yearly extravaganza.

The Getulio Vargas Foundation and consultancy Ernst and Young have said the country needs more than $11 billion in investment to fix roads, boost hotel capacity, reinforce security and develop its telecom network ahead of the Cup.