Part of the stadium that will host the 2014 World Cup opener collapsed Wednesday, killing two workers and aggravating already urgent concerns Brazil won't be ready for soccer's signature tournament.

The accident at the Arena Corinthians, known locally as the Itaquerao, could hardly have come at a worse time — just a week ahead of the draw that will determine the tournament's schedule and with the top names in soccer all descending on Brazil.

Preparations have been plagued by setbacks including cost overruns, stadium delays, accidents, labour strife and huge street protests in the run-up to the June tournament, once envisioned as a coming out party for South America's largest nation, which is also scheduled to host the 2016 Olympics in Rio de Janeiro.

Already, public prosecutors and a workers union in Sao Paulo were demanding an investigation into conditions at the venue, saying work shouldn't resume until authorities deem the stadium safe.

Ricardo Trade, CEO of the local World Cup organizing committee, said authorities would determine if there is a need to suspend construction.

"There are seven months till the World Cup, not 10 days, so I don't believe this is going to cause delays. But there is absolutely no guarantee on this," Trade said in a telephone interview.

The accident could also lead to recriminations between local organizers and world soccer's organization FIFA, which has set a December deadline for all 12 World Cup stadiums to be ready. The tournament begins June 12.

"I don't want to know about FIFA right now; we are worried about the families of the victims," said Andres Sanchez, former president of the Sao Paulo soccer club Corinthians, which is building the stadium. The club said workers will not return before a three-day mourning period.

Structure not compromised

The stadium was nearly finished before the collapse, which occurred when a construction crane crashed into a 454-tonne metal structure. That structure then cut through the outer walls of the venue, destroying part of the outside of the building and rows of seats and slamming into a giant LED panel that runs across the stadium's facade.

Sanchez said it appeared the structure of the stadium was not compromised, meaning there should be enough time to recover before the World Cup.

"Structurally very little was affected," he said.

Arena Corinthians

A view of the stadium, officially known as Arena Corinthians, under construction in August of this year 2013. The venue was close to being finished before Wednesday's collapse. (Andre Penner/Associated Press)

Six stadiums have already been declared ready for the games. But Brazil is racing against time to deliver the other six, and there is particular concern that the stadiums in Cuiaba, Manaus and Curitiba may not be ready by the end of December.

FIFA has said it would not accept the same delays that plagued stadium construction before soccer's Confederations Cup earlier this year, for which only two stadiums were ready on time.

Soccer's governing body said Wednesday that the "safety of workers is the top priority" to World Cup organizers and called on local authorities to "fully investigate the reasons behind such a tragic accident."

The Sao Paulo stadium, which cost nearly $360 million, will seat nearly 70,000 people.

It's scheduled to host six matches in all, including the opener and a semifinal. The stadium was initially expected to be built for June's Confederations Cup, but delays with financing prompted authorities to scrap the project from the World Cup warm-up tournament.

One of the dead workers, 42-year-old Fabio Luis Pereira, was inside a truck that was hit by the fallen metal structure. The other, 44-year-old Ronaldo Oliveira dos Santos, was taking a break in an area that was supposed to be clear.

"Unfortunately nobody saw him," Sanchez said. "He was napping."

The accident happened at lunchtime, so few of the nearly 1,700 workers were on the site when the crane collapsed.

"The sound was as loud as a thunderclap or a huge explosion," said Rodrigo Vessoni, a reporter with the sports newspaper Lance who witnessed the accident. "There was a lot of running around, a lot of shouting. It was frightening. Chills ran through my entire body."

A stonemason who was off at a cafeteria said it was lucky the accident happened when it did.

"If it hadn't been lunchtime there would have been many more deaths," said 32-year-old Evandro Pereira. "It was really very scary."

An official with construction company Odebrecht said a similar metal structure had already been installed with the same crane at the other side of the stadium earlier this year.

"Everything was being done according to procedure," said Frederico Barbosa, the site manager.

Problems at other facilities

It wasn't the first problem with World Cup stadiums in Brazil.

One worker died last year during construction of a stadium in the capital, Brasilia, and one was killed at the Manaus stadium last March.

Another worker died in April at the new Palmeiras stadium, which may be used for teams training for games in Sao Paulo. Construction there was stopped for 10 days for when damage that was not as serious as the destruction Wednesday at the Corinthians stadium.

Other problems have seen heavy rains flood the construction site at Rio's Maracana Stadium last March, forcing the cancellation of a FIFA inspection visit. In May, a small part of the roof at Salvador's stadium collapsed from the weight of water that accumulated during a heavy rainstorm.

In Rio, the stadium that will host track and field events in the 2016 Olympics has been closed for several months because of fears that its roof could collapse. Renovation work is underway there.