Two buildings - one almost 20 storey tall - have fall down in Rio de Janeiro, Brazil, filling streets with building material and covering cars with wreckages.
Authorities say up to 11 people are considered to be inside the buildings and five people have been saved.
The reason of the crumple remains not clear, but onlookers spoke of a huge blast and a strong smell of gas.
City Mayor Eduardo Paes said that they were concentrating on rescue endeavors before evaluating into the mishap's reason.
According to the BBC's Paulo Cabral, rescue workers were able to haul a cleaner from inside one of the pulleys in the debris after he managed to call a friend on his mobile phone.
The buildings – situated near the Municipal Theatre and the headquarters of oil gigantic Petrobras - crushed a four-storey building site on their way down.
The location adjacent the buildings are now filled up with wreckage, with many cars somewhat covered by ruins.
Numbers of emergency workers are at the site and police have cordoned off the area, our correspondent adds.
Electricity to the street has been shut down for security measures.
One observer, who known himself as Gilbert, told Reuters news agency: "It was similar to an earthquake. Initially some pieces of the buildings begin to collapse. People began to flee. And then it all collapsed immediately."
The incident comes a little over three months after an alleged gas blast at a restaurant in the city left three people deceased.
Worries have been increased about the state of Rio de Janeiro's infrastructure as Brazil ready to host football's World Cup in 2014 and the Olympic Games two years later.
