4/16 10:40 AM PT -- Notre Dame Cathedral spokesman Andrew Finot says he estimates the building will be closed to the public for at least 3 years, because the entire roof has disappeared and needs to be rebuilt entirely.

Finot says there is still standing water on the floor of the cathedral from firefighters battling the flames, but believes 80 percent of the priceless artifacts in the sanctuary were saved.

3:52 PM -- Miraculously, the interior is still standing, and the famous stone archways are still bearing weight.

However, those holes in the ceiling and the debris in front of the altar are clear signs that the restoration process, if possible at all, will be a long and difficult project.

2:15 PM -- In what might be the best news possible, under the circumstances ... the Paris police chief just said Notre Dame's structure has been saved, and the fire stopped from spreading to the northern belfry. In fact, they say both towers are going to be safe.

12:48 PM -- According to Agence France-Presse -- the international news agency based in Paris -- French fire services say they are "not sure" if the Notre Dame fire can be stopped. The deputy interior minister said saving Notre Dame "is not certain."

12:02 PM -- The fire has sadly reached the left tower. Macron also arrived on the scene moments ago. He had previously tweeted, "Our Lady of Paris in flames. Emotion of a whole nation. Thought for all Catholics and for all French. Like all our countrymen, I'm sad tonight to see this part of us burn."

11:45 AM PT -- A Notre Dame spokesperson says ... "Everything is burning, nothing will remain from the frame." Sources believe the inferno may have been caused by recent restoration of the church.

11:30 AM PT -- It is currently unknown what caused the fire or if any people were inside the church at the time. A church spokesperson has told French media all of Notre Dame Cathedral's frame is burning after the spire collapsed.

President Macron and Prime Minister Edouard Philippe are heading to the scene.

11:15 AM PT -- The cathedral's roof and famous spire has collapsed in flames. Firefighters are on the scene trying to battle the blaze, but are reportedly having major problems due to their ladders being too short to attack the fire. The cathedral's roof has also completely collapsed.

President Emmanuel Macron has canceled a national address because of the current emergency.

Notre Dame Cathedral -- one of the most popular landmarks in Paris -- is going up in flames.

Shocked and horrified tourists are posting photos and videos that show flames in and around the building's huge spire. Smoke is billowing up and filling the sky over Paris ... where prosecutors have launched an investigation to determine the cause of the fire.

Firefighters are racing to the scene, and according to one reporter, the fire might have been sparked by restoration work that's being done at Notre Dame. According to reports ... most of the art work inside the church is feared gone.

CBS News reports status of the "pieces of the cross they believe that Jesus was crucified on, as well as part of the thorned crown that he had, as well as one of the nails from the crucifixion" is unknown.

The famous church was completed in the 14th century -- nearly 200 years after breaking ground -- and is considered one of the finest examples of French Gothic architecture.

The length of time it took to build is evident in the various architectural styles throughout the building -- there are signs of the Renaissance and the Naturalism era along with the French Gothic look.

The Cathedral is one of the first buildings in the world to use the flying buttress, which artitects installed long after the original design to alleviate the wall's stress fractures that began to occur as the walls grew higher.

The Cathedral has suffered damage and deterioration over the centuries, especially during the French Revolution in 1786. It was saved from possible destruction by Napoleon, though -- who crowned himself emperor inside the cathedral in 1804 -- and later restored. Its notable central spire was actually added during restoration in the 19th century.

Along with being a famous landmark and tourist attraction, it has played host to countless religious ceremonies and historical events ... including the crowning of Henry VI of England in 1431 and the beatification of Joan of Arc by Pope Pius X in 1909.

The cathedral is the iconic setting of Victor Hugo's 1831 novel, "The Hunchback of Notre-Dame."

The Middle Ages structure gets more than 12 million visitors each year ... making it the most visited building in Paris.

One bit of good news ... 16 statues that sit atop Notre Dame -- representing the 12 apostles and 4 evangelists -- were removed just last week as part of the restoration project.