The official said investigators still do not have the green light to work in the cathedral and search in the rubble for safety reasons.
He said the monument is still being consolidated with wooden planks to support some fragile parts of the walls.
The probe was taking place as France paid a day-long tribute to the Paris firefighters who saved the famous cathedral from collapse and rescued its treasures.
The tributes came as construction workers rushed to secure an area above one of the church’s famed rose-shaped windows and other vulnerable sections of the fire-damaged landmark.
President Emmanuel 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, preventing the structure’s destruction and rescuing many of the important relics held inside.
“We’ve seen before our eyes the right things perfectly organised in a few moments, with responsibility, courage, solidarity and a meticulous organisation”, Mr Macron said. “The worst has been avoided.”
Mr Macron said the firefighters will receive a medal for their courage and devotion.
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 building would have burned to the ground in a “chain-reaction collapse” had firefighters not moved as rapidly as they did to battle the blaze racing through the building, said Jose Vaz de Matos, a fire expert with France’s Culture Ministry.
Mr Macron wants to rebuild the cathedral within five years – in time for the 2024 summer Olympics that Paris is hosting – but experts say the vast scale of the work to be done could easily take 15 years, since it will take months, even years, just to figure out what should be done.North Macedonia readies for first elections since name change