A colossal fire swept through the famed Notre-Dame Cathedral in central Paris on Monday, causing the iconic spire of the nearly millennium-old building to collapse. Here's what we know so far about how it started and the damage done to the world's most visited Cathedral.

There efforts were hampered by everything from heavy traffic around the historic site in the heart of Paris to the difficulty in accessing the raging fire high up in the roof of the building.   But questions soon began to be asked about the cause.

What do we know about how the fire broke out?

-The fire started in the attic of the Cathedral at around 18:50 local time in Paris and within minutes images and videos of the blaze were being shared around the world.

A spokesman for the Cathedral reported that a fire alarm went off almost immediately and they instantly recognised it because they had practised a fire drill just days before. Smoke could be seen immediately bellowing from the attic.

Built between the years 1163 and 1345, Notre-Dame is one of the most popular tourist sites in Paris, drawing around 13 million people every year.The spire, like the rest of the gothic edifice, had been undergoing the 11-million-euro ($12.4-million) overhaul financed by the French state to repair damage inflicted by time, pollution and the weather.The fire service did say early on that the blaze could be "potentially linked" to ongoing renovations.However reports in the French media said there wasn't any work taking place at the time the blaze began because workmen had finished for the day.

Were there any victims?

As of Monday evening there were no reported victims but the Cathedral's spokesman said they couldn't say for certain.

Many, including Donald Trump asked the question why a water plane or helicopter couldn't fly over Paris and drop tons of water on the fire just like in the case of forest fires.

The reality is that these planes are not geared towards dropping water on such a small area and the weight of the water dropped in all one go could cause part of the structure to collapse.

"Dumping water from a plane on this type of building would risk bringing down the whole edifice," France's Civil Security agency wrote on Twitter.

What damage has the blaze caused to the Cathedral?

We know so far that the spire of the Cathedral and the roof collapsed. According to the Cathedral's spokesman "the whole frame of the roof of the Cathedral was burning".

"The roof's frame dates from the 19th century on one side and the 13th century on the other. There's nothing left," said the spokesman.

"We need to see whether the vault, which protects the Cathedral has been damaged or not."

The Holy Crown of Thorns and a sacred tunic worn by 13th-century French king Louis, two irreplaceable artifacts, had been rescued, the cathedral rector Patrick Chauvet said.

There were more positive reports on Twitter however, although unconfirmed that stated the treasures and artworks stored in the cathedral had been saved.But by about 23:00 on Monday evening the fire service said the Cathedral's main frame had been saved and the structure preserved.

French president Emmanuel Macron said the worst had been avoided thanks to firefighters "although the battle is not yet totally won".

Macron vowed that "we will rebuild Notre-Dame together".