The fire, declared fully extinguished some 15 hours after it began, ravaged the 850-year-old building's roof and caused its spire to collapse.

But firefighters who worked through the night managed to save the Paris landmark's main stone structure, including its two towers.

The cause of the fire is not yet clear.

Paris public prosecutor Rémy Heitz said his office was "favouring the theory of an accident", but had assigned 50 people to work on what he believed would be a "long" and "complex" investigation. Other officials have suggested it could be linked to extensive renovation works taking place at the cathedral.

For centuries the building has been considered the heart of Catholic life in France, a site of pilgrimage for people around the world and home to many priceless religious relics.

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