France to investigate Madonna stage collapse that killed 2

French prosecutors announced Friday they have opened a manslaughter investigation into the stage collapse in Marseille that killed two workers ahead of a weekend concert by Madonna.

Initial hearings will take place Sunday or Monday, conducted by the prosecutor's office for manslaughter and involuntary injuries in work-related accidents, assistant prosecutor Marc Simamonti said.

A French worker died instantly and a British worker later died a local hospital from injuries suffered in the incident, which occurred Thursday at the Stade Velodrome in the southern French port city. A partially completed roof section of the complex and an intricate set collapsed on top of several people.

Eight others were injured in the accident, with one in critical and four in serious condition, officials said.

Though it was initially noted that an American was among those in serious condition, authorities have confirmed that the remaining casualties are all French citizens.

Sunday's Marseille concert has been cancelled.

Singer 'devastated' by accident

Madonna was reportedly "devastated" when she learned of the incident while warming up for her concert in Udine, Italy, on Thursday.

The singer later paid tribute to the deceased and injured workers while on stage, breaking out in tears as she shared news of the incident with the audience and asking fans to take "a moment to stop and to stop and think of the people who have lost their lives. We need to appreciate life, the people we love and our families."

She also issued a statement, sending her "prayers... out to those who were injured and their families, along with my deepest sympathy to all those affected by this heartbreaking news."

Since last summer, Madonna has been travelling the world performing her Sticky and Sweet tour in support of her 2008 album Hard Candy.

Music trade magazine Pollstar named the Sticky and Sweet world tour the top concert attraction of 2008, earning Madonna $281.6 million US last year.

It also helped vault the entertainer to the top of Billboard magazine's 2008 annual list of the top music world money-makers.