PARIS — Bells of cathedrals across France rang in a moving tribute Wednesday to Notre Dame as firefighters and experts continued to keep the beloved but weakened landmark under close surveillance.

From Sacre Coeur in Paris to the cities of Strasbourg in the east and Rouen in the west, the architectural treasures of France solemnly marked the inferno, two days after it ravaged the gothic cathedral, widely regarded as the soul of France.

“I just arrived for the first ring of the bells and immediately there was an emotion. Incredible, indescribable, I just can’t explain it,” said Nadia Pascassio-Comte, in Strasbourg. “It was beautiful and sad at the same time. I had tears in my eyes at one point, and I think that this solidarity is magical, it really unites a lot of people.”

At Saint Sulpice church, the second-largest house of worship in Paris, French first lady Brigitte Macron attended a special service for the annual blessing of the oils during Holy Week, ahead of Easter Sunday.

Meanwhile, restoration specialists questioned President Emmanuel Macron’s ambitious five-year reconstruction timeline for Notre Dame, with some suggesting it could take more than three times that amount of time to rebuild the 850-year-old architectural treasure.

Even Prime Minister Edouard Philippe acknowledged Wednesday that it would be difficult.

“This is obviously an immense challenge, a historic responsibility,” Philippe said after a Cabinet meeting focused on the restoration.

Prominent French conservation architect Pierluigi Pericolo told Inrocks magazine the restoration work could take “no less than 15 years. … It’s a colossal task.”

Pericolo, who worked on the restoration of the 19th-century St.-Donatien Basilica, which was badly damaged in a 2015 blaze in the French city of Nantes, said it could take two to five years just to check the stability of Notre Dame, which dominates the Paris skyline.