Flames and smoke are seen billowing from the roof at Notre-Dame Cathedral in Paris on April 15, 2019. - A fire broke out at the landmark Notre-Dame Cathedral in central Paris, potentially involving renovation works being carried out at the site, the fire service said.Images posted on social media showed flames and huge clouds of smoke billowing above the roof of the gothic cathedral, the most visited historic monument in Europe. (Photo by Fouad Maghrane / AFP)

The steeple of the landmark Notre-Dame Cathedral collapses as the cathedral is engulfed in flames in central Paris on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by Geoffroy VAN DER HASSELT / AFP)

The steeple collapses as smoke and flames engulf the Notre-Dame Cathedral in Paris on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by Geoffroy VAN DER HASSELT / AFP)

A man watches the landmark Notre-Dame Cathedral burn, engulfed in flames, in central Paris on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by Geoffroy VAN DER HASSELT / AFP)

Smoke and flames rise during a fire at the landmark Notre-Dame Cathedral in central Paris on April 15, 2019, potentially involving renovation works being carried out at the site, the fire service said. - A major fire broke out at the landmark Notre-Dame Cathedral in central Paris sending flames and huge clouds of grey smoke billowing into the sky, the fire service said. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year, where renovations are currently underway. (Photo by FRANCOIS GUILLOT / AFP)

Flames and smoke are seen as the interior of the Notre-Dame Cathedral continues to burn on April 15, 2019, in the French capital Paris. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by PHILIPPE WOJAZER / POOL / AFP)

People react as they watch flames engulf the roof of the Notre-Dame de Paris Cathedral in the French capital Paris on April 15, 2019. - A colossal fire swept through the famed Notre-Dame Cathedral in central Paris on April 15, 2019, causing a spire to collapse and threatening to destroy the entire masterpiece and its precious artworks. The fire, which began in the early evening, sent flames and huge clouds of grey smoke billowing into the Paris sky as stunned Parisians and tourists watched on in sheer horror. (Photo by GEOFFROY VAN DER HASSELT / AFP)

Flames and smoke are seen billowing from the roof at Notre-Dame Cathedral in Paris on April 15, 2019. - A fire broke out at the landmark Notre-Dame Cathedral in central Paris, potentially involving renovation works being carried out at the site, the fire service said. (Photo by Thomas SAMSON / AFP)

Flames and smoke are seen billowing from the roof at Notre-Dame Cathedral in Paris on April 15, 2019. - A fire broke out at the landmark Notre-Dame Cathedral in central Paris, potentially involving renovation works being carried out at the site, the fire service said.Images posted on social media showed flames and huge clouds of smoke billowing above the roof of the gothic cathedral, the most visited historic monument in Europe. (Photo by Fouad Maghrane / AFP)

A woman cries as people look at Notre-Dame de Paris Cathedral engulfed in flames from the Paris's Hotel de Ville esplanade on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. (Photo by STR / AFP)

Firefighters douse flames rising from the roof at Notre-Dame Cathedral in Paris on April 15, 2019. - A major fire broke out at the landmark Notre-Dame Cathedral in central Paris sending flames and huge clouds of grey smoke billowing into the sky, the fire service said. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year, where renovations are currently underway. (Photo by Bertrand GUAY / AFP)

Flames are doused through the scaffolding erected on the roof of the Notre-Dame de Paris Cathedral after a fire broke out on April 15, 2019, in the French capital Paris. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by STEPHANE DE SAKUTIN / AFP)

Firefighters douse flames rising from the roof at Notre-Dame Cathedral in Paris on April 15, 2019. - A major fire broke out at the landmark Notre-Dame Cathedral in central Paris sending flames and huge clouds of grey smoke billowing into the sky, the fire service said. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year, where renovations are currently underway. (Photo by LUDOVIC MARIN / AFP)

People kneel on the pavement as they pray outside watching flames engulf Notre-Dame Cathedral in Paris on April 15, 2019. - A colossal fire swept through the famed Notre-Dame Cathedral in central Paris on April 15, 2019, causing a spire to collapse and raising fears over the future of the nearly millenium old building and its precious artworks. The fire, which began in the early evening, sent flames and huge clouds of grey smoke billowing into the Paris sky as stunned Parisians and tourists watched on in sheer horror. (Photo by ERIC FEFERBERG / AFP)

Fire fighter douse the Notre-Dame de Paris Cathedral after a fire broke out on April 15, 2019, in the French capital Paris. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by STEPHANE DE SAKUTIN / AFP)

Firefighters (below) work to extinguish a fire at Notre-Dame Cathedral in Paris early on April 16, 2019. - A huge fire that devastated Notre-Dame Cathedral is "under control", the Paris fire brigade said early on April 16 after firefighters spent hours battling the flames. (Photo by STEPHANE DE SAKUTIN / AFP)

People hug while looking at Notre-Dame-de-Paris on April 16, 2019 in the aftermath of a fire that devastated the cathedral. - Paris was struck in its very heart as flames devoured the roof of Notre-Dame, the medieval cathedral made famous by Victor Hugo, its two massive towers flanked with gargoyles instantly recognisable even by people who have never visited the city. (Photo by Bertrand GUAY / AFP)