“It’s very hard for everyone, it’s yet another blow,” Mr. Finot said by telephone on Monday.

President Emmanuel Macron of France vowed after the fire that Notre-Dame would be rebuilt in five years, a tight deadline that the authorities are sticking to so far.

Jean-Louis Georgelin, an army general nominated by Mr. Macron to lead the task force in charge of reconstruction, promised this month that a religious service would be held inside Notre-Dame on April 16, 2024, exactly five years after the fire, to “celebrate the work that will have been done.”

Recovery efforts continue at the cathedral, which was added in October to the 2020 World Monuments Watch, a biennial list of cultural heritage sites that are in urgent need of conservation.

The authorities caution that Notre-Dame is in an extremely precarious state and in need of constant monitoring to ensure parts of it do not collapse. The vault is still punctured by gaping holes, and the flying buttresses are propped up by giant wooden blocks.

But the most urgent threat to Notre-Dame is thousands of scaffolding tubes — remnants of renovation work from before the fire — that were welded together by the blaze, creating a mass of twisted metal of roughly 250 tons that is weighing down on the structure.