The accident, which sent victims tumbling 50 feet to the ground amid twisted and broken scaffolding, cast a shadow over celebrations planned for next month ahead of the sold-out January maiden voyage of the world's largest and most expensive oceanliner.
Two people died overnight from their injuries in Saturday's fall, bringing the death toll to 15, officials at the company building the ship said. A child about 10 years old was among the dead.
About 30 others were injured, with some hospitalized in serious condition. Many of the casualties were visiting family members of the workers building the ship, which is dry-docked at this Atlantic coast shipyard for finishing touches before the launch.
Mourners left bouquets of flowers outside the gate of the shipyard. Fabrice Ponchaux, 32, lost his mother and his aunt in the collapse, and his father was in the hospital.
"This ship should have been our national pride," Ponchaux said.
One distraught woman sobbed repeatedly, "Why didn't they put in a net?"
As 48 people crowded onto the gangway, the structure collapsed, pulling down scaffolding holding it up at one end and sending people plunging 50 feet to the pavement below.
Survivors described chaos and trauma.
"At the bottom, everyone was screaming, and blood was everywhere," said Jessica, 21, who went on France-2 television with swollen eyelids and bruises covering her face. Her last name was not given.
Some officials had put the number of deaths at 16. However, the local prosecutor and Patrick Boissier, president of Chantiers de l'Atlantique, which is building the ship, said later that 15 people had died.
The gangway was installed Friday for a weekend visit by construction workers and their families of the nearly complete oceanliner. About 2,600 workers board and leave the ship every day.
Patrick Boissier, president of Chantiers d'Atlantique, said it was still unclear what caused the gangway to buckle.
"It's too early to say what happened," he said. "There will be an investigation."
Philippe Venet, director of Endel, which built the plank, said the company has set up similar structures for Chantiers d'Atlantique for years. He also said the cause of the accident was unclear.
Local leaders had planned a series of celebrations late next month, but the accident raised doubt about whether such festivities would go on.
"Naval construction is a family that knows how to share its glories and its difficult moments," St. Nazaire mayor Joel Batteux told regional L'Eclair Dimanche newspaper. "But it's never been as hard as this."
"We were preparing an important event, but now, it's out of the question to celebrate," he said.
The accident was the latest blow for the company that built the ship. France's Alstom is heavily in debt and awaiting European Union clearance on a multibillion euro bailout package from the government.
The Queen Mary 2 is the world's largest passenger ship at 1,138 feet long and 238 feet high — as tall as a 21-story building.
It is also the most expensive, costing $800 million to build. Once completed, the Queen Mary 2 will feature a planetarium, 22 elevators and the world's largest floating library.
The shipyard was to be closed Monday for a day of mourning.
Flags flew at half-staff over police stations and the concrete city hall in St. Nazaire, which lives off heavy industries such as ship and airplane construction.
Britain's Cunard Lines, which operates the vessel and is owned by Miami-based Carnival Corp. in the United States, said the maiden voyage from Southampton, England, to Fort Lauderdale, Fla., would likely go ahead as planned.
"To the best of our knowledge, the ship will sail Jan. 12, as scheduled," said Julie Davis, a spokeswoman in Miami for Cunard.
Cunard Lines issued a statement Saturday offering "thoughts and prayers" for the victims and their families. It made no comment on the accident itself.
French President Jacques Chirac and Prime Minister Jean-Pierre Raffarin were to visit the shipyard Sunday.
The accident came just four days after ship completed its second successful sea trial. The first was in September.