Paris, April 16 -- A massive fire engulfed the roof of Notre Dame Cathedral in the heart of the French capital Monday, toppling its spire and sending thick plumes of smoke high into the blue sky as tourists and Parisians watched in horror from the streets below.

A spokesman said the entire wooden frame of the cathedral would likely come down, and that the vault of the edifice could be threatened too.

"Everything is burning, nothing will remain from the frame," Notre Dame spokesman Andre Finot told French media. The 12th-century cathedral is home to incalculable works of art and is one of the world's most famous tourist attractions.

The cause of the catastrophic blaze was not known, but French media quoted the Paris fire brigade as sayi...