The fire is "potentially connected" to ongoing renovations in the historic building.
According to a Fire Brigade source, the fire is "potentially linked" to the restoration work in Notre-Dame de Paris, in the center of the French capital.
While it is not yet possible to understand the severity of the fire, firefighters have also said that the fire originated on the roofs of the cathedral, the most visited monument in Europe.
According to the Notre-Dame de Paris' spokesman, the fire started at 6:50 p.m. local time.
"A terrible fire is taking place in the Notre-Dame de Paris. The Paris Fire Brigade is fighting the flames. We are mobilized on the spot, in close collaboration with the diocese of Paris. I urge everyone to respect the security perimeter," wrote on Twitter Mayor Anne Hidalgo.
The same appeal is made by the municipal police, through Twitter, asking people to avoid this area of the city and to give way to the emergency vehicles involved in fighting the fire in the iconic building.
The restoration work began last Wednesday, April 10, when the 16 copper statues, three meters high, which stood on the shaft of the Cathedral, an architectural element with 96 meters, were removed.
This stage marks the beginning of the huge renovation work on the entire 96 m shaft, which has undergone many changes over the centuries. The end of the work, worth six million euros and financed by the State and sponsors, was planned for 2022.
"Sad to see a part of us burn," Emmanuel Macron wrote on Twitter, at a time when the French president is expected at the location, postponing the communication to the country that was scheduled for 8 p.m., on Monday.