The accident occurred at Chantiers de l'Atlantique, the French shipyard where the vessel is in final construction phases.
News reports say that the victims were family members of shipyard workers who had been invited for the day to tour the ship. Also visiting the Queen Mary 2 was a host of dignitaries.
A temporary mortuary has been set up at the shipyard. French president Jacques Chirac visited the site Sunday. A prosecutor has opened a criminal investigation into the accident.
Cunard has issued a statement from company president Pamela Conover expressing condolences. The shipyard is closed today in mourning. Cunard officials have said they do not expect this to delay the ship's delivery, scheduled for December 25, or its maiden voyage, in mid-January.