Aftermath of the stage collapse at the 60,000 seater Velodrome
Prosecutors have opened a manslaughter investigation after a stage being built for a Madonna concert collapsed killing two people, a French official has said.
Eight other people were seriously injured in Thursday's accident at the Velodrome stadium in Marseille.
Assistant prosecutor Marc Cimamonti said an investigation for manslaughter and involuntary injuries in a work-related accident has been opened.
Madonna has said she is "devastated" by the news of the deaths.
Her concert, planned for Sunday, has been cancelled.
Charles Criscenzo, a 53-year-old French worker, was killed outright in the accident and Charles Prow, a 23-year-old from Headingley in Leeds, died in hospital.
Technicians had been setting up the stage at the city's Velodrome stadium when the partially-built roof fell in on Thursday, bringing down a crane.
The 60,000-seater Velodrome is France's second-biggest sports arena and home to the Olympique de Marseille football club.
The planned concert was part of Madonna's Sticky and Sweet tour
About 50 people from a range of nationalities were working to set up the structure, city sports official Richard Miron said.
The roof "started shaking and collapsing" gradually, said Marseille city councillor Maurice Di Nocera.
"Since it did not collapse right away that allowed several people to get out," he said.
Madonna, who is performing on her Sticky and Sweet tour, was in Udine, Italy, when told of the incident.
"I am devastated to have just received this tragic news," she said in a statement released by Live Nation, the organisers of the concert.
"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."
Madonna paid tribute to the technicians at her concert in Italy on Thursday.
"I just wanted to take a moment to acknowledge and pay tribute to two people who lost their lives today," she told fans at the Fruili Stadium in Udine.
"It's a great tragedy to me," she continued, choking back tears. "I feel so devastated to be in any way associated with anyone's suffering.
"Let's all just take a moment to say a prayer for Charles Criscenzo and Charlie Prow. Our hearts go out to their family and loved ones."