City chiefs have shut down the Rio de Janeiro stadium which will host the athletics events at the 2016 Olympics because of potentially dangerous structural problems with its roof.
Authorities said the Joao Havelange Stadium, known locally as the Engenhao, was not safe to host public events until the problems were fixed.
Rio de Janeiro mayor Eduardo Paes said he decided to close the venue immediately after builders monitoring the stadium's roof informed him of the structural problems.
"I asked them if these problems posed a threat to fans and the answer was yes, depending on circumstances such as wind velocity and temperature," Mr Paes said.
"There was a risk so I decided to close the stadium immediately until we have more details about the solution that we will need."
Mr Paes said the extent of the threat was not fully known, but the decision was based on three different reports which showed that the structural problems presented risks. A more complete analysis will take place before solutions can be considered.
"The stadium will stay closed for an undetermined period," the mayor said. "If they give me a solution that will last a month, then it will stay closed for a month, if it takes a year, it will stay closed for a year. I will wait until a definitive solution if presented. We can't play with something like this."
Local Olympic organisers played down the possibility that the problem would affect the 2016 Rio Games, saying the event was still "years" away and that a solution would probably be found long before the first Olympics in South America.
"The Rio 2016 Olympic and Paralympic Organising Committee has full confidence that the city of Rio de Janeiro will take the necessary measures to guarantee that the Olympic Stadium is ready for the Games more than three years from now, as well as for the test events before them," the organising committee said in a statement.
Mr Paes said officials would investigate what caused the problem so those responsible could be held accountable. He said it could be an issue linked to the original project of the stadium. The Engenhao has been the main Rio stadium since the Maracana closed for renovation ahead of the Confederations Cup and the 2014 World Cup. It will not host matches in those tournaments, but it could be used for training.