Notre Dame cathedral's two historic bell towers have been saved from collapse after firefighters halted the spread of the flames.
The update came after officials earlier warned that firefighters may not be able to stop the huge blaze which tore through the cathedral.
Speaking outside the cathedral, fire chief Jean-Claude Gallet had told reporters he was "not sure we are capable of stopping the spreading" to Notre Dame's second tower and belfry.
But he later confirmed the belfry had been saved, but two-thirds of the 850-year-old Gothic building's roof "has been ravaged" - and the spire was seen collapsing in the smoke.
Fire crews will keep working overnight to cool down the structure, Mr Gallet added.
Concerns over the scale of the damage to Notre Dame came as expressions of grief were sent to Paris from around the world.
Notre Dame fire: Firefighter seriously injured as Paris cathedral burns
French President Emmanuel Macron sent out his thoughts for "all Catholics and to the French people".
"Notre Dame is aflame," he said.
"Great emotion for the whole nation. Our thoughts go out to all Catholics and for to the French people. Like all of my fellow citizens, I am sad to see this part of us burn tonight."
Prime Minister Theresa May sent her wishes to the French capital from her walking holiday with her husband in Wales, where she is spending the beginning of parliamentary recess.
"My thoughts are with the people of France tonight and with the emergency services who are fighting the terrible blaze at Notre Dame cathedral," she said.
Meanwhile, US President Donald Trump tweeted some advice for the Paris Fire Brigade, suggesting "flying water tankers" to put out the flames.
The fire began on Monday evening, with first reports emerging of smoke in the cathedral shortly before 6pm.
The last visitors of the day were evacuated and the Paris Fire Brigade began to fight flames which had emerged from the cathedral's roof.
A French official said that while the source of the fire was unknown, it could be linked to renovation works to fix Notre Dame's historic stone walls and buttresses.
The fire first brought down the cathedral's 315ft (96m) spire, and has spread to one of its two towers, which form its famed frontage.
Notre Dame is one of the city's oldest and most recognisable buildings, and work began on it in 1163.
The original structure was completed nearly 200 years later, in 1345, and its name literally translates to "Our Lady of Paris".
Some 13 million people now visit the Catholic landmark every year - more than 30,000 every day on average - according to its official website, and it is believed to be the most visited structure in the French capital.
Its renovation works were estimated to cost around 150 million euro (£130 million).
