A janitor finishing up the day's work, an accountant closing the books for the month, a computer technician installing software: each had a reason to stay a little late at work.

They were among those trapped when three buildings suddenly collapsed into a pile of rubble in downtown Rio de Janeiro. Rescuers pulled out at least six bodies, according to the city morgue, and 16 people remained missing Thursday as the smoke from small fires drifted above the wreckage.

Authorities are still investigating the cause, but officials speculated that illegal construction work damaged the structure of a 20-storey building and caused it to crumble, wrenching down two other office buildings alongside at about 8:30 p.m. Wednesday.

The janitor was among the six injured extracted by rescue crews from the heap of bricks, metal and glass. The accountant and the computer technician are among the missing. Their friends or relatives took shelter from the scorching sun in a nearby building, hoping for news.


Rescue workers stand next to three collapsed buildings in Rio de Janeiro, Brazil. A 20-storey building collapsed in Rio's centre Wednesday evening, causing the collapse of other two smaller ones. (Associated Press/Silvia Izquierdo)

"Firefighters and others are working to find the missing," said Moises Torres, a spokesman with the fire department who confirmed the numbers of dead and missing. "We have hopes of finding people alive."

The accident could have been much worse, the CBC's Latin America correspondent, Connie Watson, reported from Rio. Most of the buildings' tenants were businesses that were closed for the day when the tower tumbled on to the two smaller buildings, she said.

One witness said that, at first, someone was "just throwing rubble."

"Then, all of a sudden, the building collapsed. It came down completely. It looked like Sept. 11 here," he said in Portuguese.

Illegal construction in collapsed building

A building inspector told the Globo television network that a survivor from the collapse was a worker on a construction project being performed in the first building that went down, and that illegal projects could have led to the collapse.

"Two projects were happening in the building, on the 16th floor," said Luiz Cosenza, head of the accident prevention unit of Rio's Regional Council of Engineering, in charge of building inspections. "They were illegal works; they were not registered with the council."

He didn't provide details on what sort of construction work was being carried out, but said that it was not being supervised by any registered professional.

'Structural damages' to blame: mayor

Shortly after the collapse, there was a strong smell of natural gas in the area, but Mayor Eduardo Paes said that probably did not cause the problem.

"There apparently was not an explosion. The collapse occurred because of structural damages," he said. "I don't think there was a gas leak."

On Thursday, relatives and friends of the missing gathered inside a nearby government building, taking shelter from from the scorching sun as they waited for news.

'We think he's alive. At 3 a.m. he managed to call his girlfriend … the family is hanging all their hopes on that phone call.'  —Francisco Adir, whose friend is missing after the collapse

Francisco Adir was trying to get information about a friend who had been attending a computer course in the in the largest of the three buildings.

"We think he's alive. At 3 a.m. he managed to call his girlfriend and say, 'Hello, love," before his phone went dead," Adir said. "The rescuers haven't given us any information, but the family is hanging all their hopes on that phone call."

Rio is scheduled to host soccer's World Cup in 2014 and the Summer Olympics in 2016. Failures of infrastructure such as Wednesday's building collapse are raising concerns about whether the city is ready for the thousands of people who will descend on it for those international events.

With files from the CBC