Two workers were killed when a crane collapsed at the stadium staging the opening match of next year's Football World Cup, causing damage to the exterior and renewing questions about whether Brazil will be ready to host the event on time.
Construction workers had been racing to finish the stadium in Sao Paulo, Brazil's biggest city, prior to a December deadline imposed by world football body FIFA.
Andres Sanchez, a former president for the Corinthians club who is helping oversee construction, told reporters that a crane collapsed while lifting a piece of the stadium's roof into place, sending the piece tumbling down.
He said the cause of the accident was still unclear and said any possible delay to construction was "the least of our worries."
The union representing the workers said it expected construction would be frozen for up to 30 days while authorities investigate.
Two workers at the site were killed, Sanchez said, with no additional casualties. Emergency officials had previously given conflicting information on the death toll and possible injuries.
The incident casts yet another shadow over Brazil's preparations for the World Cup, which have been plagued by delays, accidents, cost overruns, and public anger over government waste that contributed to massive nationwide street protests last year.
Workers have now been killed at three World Cup stadiums - in Sao Paulo, Brasilia, and Manaus. Officials have expressed worries about facilities in Manaus and Cuiaba being ready by a December deadline, and Wednesday's accident seems likely to delay Sao Paulo as well, though it's unclear for how long.
The Sao Paulo stadium, formally called Arena Corinthians but known locally as Itaquerao for the area where it is located, was 94 percent complete at the time of the accident, according to the stadium's website. The facility is due to host the Cup's opening match on June 12 next year.
Sanchez said the accident did not cause structural damage to the stadium's stands, which likely would have caused the most extensive delays to construction. A statement by Corinthians, which will play in the facility after the cup, said the piece of roof fell on top of the concourse area on the eastern side of the stadium, "partially hitting the facade."
Photos and TV images from the scene showed a huge piece of white scaffolding smashed through the exterior, collapsing the top half in the area where it hit.
It was not clear if the damage would pose a major delay to opening the stadium, according to Ricardo Trade, executive director of the local organizing committee for the World Cup.
"It's impossible to make any forecasts at this moment," Trade said. "What we know is what the images are showing, that part of the structure fell down."
"At the same time, we can't think that if (construction) is delayed by three months, the stadium will end up out of the World Cup."