Investigators probe Notre-Dame inferno as donations pour in

French investigators interviewed construction workers involved in renovation work at the Notre-Dame cathedral on Tuesday as they sought to identify the source of a devastating blaze at the monument that has sent shockwaves through France and the world.

Donations and offers of help began to pour in as day broke over the City of Light, revealing the extent of the damage from Monday night's inferno which took around 15 hours to extinguish.

"All night long I saw men going past with tears in their eyes. I described it this way: It was total chaos, but we can't let it knock us down," said Philippe Marsset, the vicar general of Notre-Dame.

Most of the roof has been destroyed, the steeple has collapsed and an unknown number of artifacts and paintings have been lost, but the walls, bell towers and the most famous circular stained-glass windows remain in tact.

Around 400 firefighters battled through the night to control the flames and the last remnants of the inferno were extinguished at around 10 am on Tuesday, 15 hours after it broke out.

Ongoing renovation work is widely suspected to have caused the fire after the blaze broke out in an area below scaffolding.

Investigators interviewed witnesses overnight and began speaking to the employees of five different construction companies which were working on the monument, said public prosecutor Remy Heitz.

"Nothing indicates this was a voluntary act," Heitz told reporters, adding that 50 investigators had been assigned to the case.

French President Emmanuel Macron had struck a defiant tone on Monday night as he visited the scene with his wife Brigitte, telling reporters: "We will rebuild Notre-Dame because it is what the French expect."