“When you see the work that’s been done over the last week, it’s colossal,” he said, citing the stabilization of some of the fantastical sculptures by the 19th-century architect Viollet-le-Duc and the securing of critical gable supports.

“It’s a huge amount of work, and we’re working everywhere,” Mr. Villeneuve said.

Already, the context for rebuilding the cathedral has shifted. The initial shock and feeling of national solidarity have partly given way to a series of quarrels.

There are those who want Notre-Dame to be rebuilt exactly as it was, including the attic with its “forest” of timbers. Yet architects have pointed out that Notre-Dame before the fire was in many respects a 19th-century rendering — via Mr. Viollet-le-Duc’s reimaginings — of a medieval building.

Then there are those who think modern elements should be incorporated in the reconstruction, including perhaps a glass roof like the one at the Grand Palais, the exhibition hall and museum complex at the Champs-Élysées.

Complicating it all is President Emmanuel Macron’s vow to rebuild the cathedral in five years, a target that some French architects say is impossibly soon, while others call it reasonable.

There is also bitterness over the pledged donations of hundreds of millions of euros by luxury trade industrialists like Bernard Arnault and François Pinault for the rebuilding. Some of those demonstrating in Paris on Saturday as part of the “Yellow Vest” movement calling for greater economic equality bore placards complaining that the pledged money was going to the cathedral rather than to people like them.

Investigators from the Paris prosecutor’s office are still trying to determine the cause of the fire.

After interviewing dozens of workers, witnesses, security guards and construction company officials, investigators think it may have been caused by a short circuit linked to the restoration work that was underway when the fire broke out, perhaps connected to the wiring of the elevators that had been installed in the scaffolding, according to French news media reports.