Madonna visited on Sunday workers injured while building a stage for her concert in southern France, as well as meeting the family of one of two workers killed in the accident.

A French worker was killed on the spot on Thursday when part of the roof over the stage being built for the pop singer's concert collapsed while a British worker died in hospital a day later. Eight other workers were injured, five seriously, and are being treated at two hospitals.

The concert had been scheduled for Sunday, but it was canceled immediately after the incident.

"We are very touched that an actress (and musician) with such talent and quality has also an extraordinary amount of human qualities as well," Marseille Mayor Jean-Claude Gaudin told reporters outside one hospital.

"She has already gone to Aix-en-Province, I think, to see the family of this worker who unfortunately has died. And, she comes here to the hospital in Marseille to meet the injured. So, we are very touched."

Marseille public prosecutors have launched an inquiry into the deaths at the Velodrome stadium. A police source said one of the four cranes used to erect the stage slipped, causing the roof to buckle.

Madonna, who was in Italy at the time of the accident, issued a statement saying she was devastated by the news and expressed her deepest sympathies to all those affected.

Marseille city authorities said all the victims worked for Live Nation, the company which was preparing the show.

The next stop on Madonna's "Sticky and Sweet" tour is scheduled for Barcelona, Spain on Tuesday, July 21.