Eight other people, some of them part of Madonna's traveling Sticky and Sweet stage crew, remain hospitalized in serious condition, including an American, according to hospital officials.
"I am devastated to have just received this tragic news," the singer said in a statement through her spokesperson Liz Rosenberg. "My prayers go out to those who were injured and their families along with my deepest sympathy to all those affected by this heartbreaking news."
The Velodrome, a 66,000-seat venue near the sea just outside the city center, was closed to the public after the accident and a police investigation into the cause was ongoing at the scene Friday morning, says a spokeswoman for the mayor's office.
'Nightmarish' SceneFiremen who arrived at the scene shortly after 5:15 p.m. Thursday described a nightmarish and chaotic scene inside the stadium, where one of four cranes lifting the stage set roof apparently snapped, sending everything crashing to the stage.
"I saw this big mess of twisted metal and cable and debris and men screaming," Thierry Delorme, a spokesman for the Marseille Fire Department, who was among the first at the scene, tells PEOPLE. "There were at least 50 workers there and many of them were trying to save their colleagues by dragging them out from under the stage."
Two workers were trapped underneath the stage set, Delorme said. More than 30 other workers were treated for shock and injuries by rescuers at the stadium, he said.
During the Italian leg of Madonna's tour, reports the Times of London, the singer broke down in tears and told the audience she was "devastated" and added, "I ask you for a moment to stop and think of the people who have lost their lives, we need to appreciate life, the people we love and our families."