FIFA president Sepp Blatter has said he is "deeply saddened" by reports that three people have died in the partial collapse of the Arena Corinthians in Sao Paulo, which is due to stage the opening match at next year's World Cup.
Hosts Brazil are due to play in the opening match at the stadium on June 12, 2014, against opponents to be determined at next month's draw.
The stadium is also due to stage five further matches, including a semi-final.
A source at the Local Organising Committee confirmed there had been fatalities but would not be drawn on the number, nor on the implications of the collapse, or its cause.
FIFA president Sepp Blatter said on Twitter: "I'm deeply saddened by the tragic death of workers @Corinthians arena today. Our heartfelt condolences are with the families."
FIFA general secretary Jerome Valcke added: "Extremely shocked by the news from Sao Paulo. Our thoughts are with the families of the victims of this accident.
"We are currently awaiting further details from the authorities, who are investigating this tragic accident."
FIFA was preparing an official statement on the events that occurred at lunchtime in Brazil.