Photo: The Canadian Press

A fire fighter makes his way on a balcony of Notre Dame cathedral Wednesday, April 17, 2019 in Paris.

Paris police investigators think an electrical short-circuit most likely caused the fire at Notre Dame Cathedral, a police official said Thursday, as France paid a daylong tribute to the firefighters who saved the world-renowned landmark.

A judicial police official told The Associated Press that investigators made an initial assessment of the cathedral Wednesday but don't have a green light to search Notre Dame's charred interior because of ongoing safety hazards.

The cathedral's fragile walls were being shored up with wooden planks, said the official, who spoke on condition of anonymity because he wasn't authorized to speak by name about an ongoing investigation.

Investigators so far believe the fire was accidental, and are questioning both cathedral staff and workers who were carrying out renovations. Some 40 people had been questioned by Thursday, according to the Paris prosecutor's office.

The police official would not comment on an unsourced report in Le Parisian newspaper that investigators are looking at whether the fire could have been linked to a computer glitch or the temporary elevators used in the renovation work, among other things. The prosecutor's office said only that "all leads must be explored."

Since the cathedral will be closed to the public for years, the rector of the Catholic parish that worships there has proposed building a temporary structure on the plaza in front of the gothic-era landmark, and City Hall gave its approval Thursday "subject to technical restraints."

"The rector has no cathedral for the moment. .... But I'm going to try to invent something," Bishop Patrick Chauvet said.

A crypt containing vestiges dating from antiquity is located under the vast esplanade.

President Emmanuel Macron has said he wants Notre Dame to be restored in five years, a timeline that restoration specialists have questioned as overly ambitious, with some saying it could take three times that long to rebuild the 850-year-old architectural treasure. Macron hopes to reopen the cathedral in time for the 2024 Summer Olympics, which Paris is hosting.

Earlier Thursday, Macron held a ceremony at the Elysee Palace to thank the hundreds of firefighters who battled the fast-moving fire at Notre Dame for nine hours starting Monday evening, preventing the structure's destruction and rescuing many of the important relics held inside.

"We've seen before our eyes the right things perfectly organized in a few moments, with responsibility, courage, solidarity and a meticulous organization", Macron said. "The worst has been avoided."

The cathedral's lead roof and its soaring spire were destroyed, but Notre Dame's iconic bell towers, rose windows, organ and precious artworks were saved.

Macron said the firefighters will receive an Honor Medal for their courage and devotion.

Paris City Hall also held a ceremony in the firefighters' honour Thursday afternoon, with a Bach violin concert, two giant banners strung from the monumental city headquarters and readings from Victor Hugo's "The Hunchback of Notre Dame."

Remarkably, no one was killed in the blaze that broke out as the cathedral was in the initial stages of a lengthy restoration.