From The New York Times:
The doors of the cathedral shut just before a last rush of tourists tried to get inside, witnesses said, and not long afterward smoke could be seen rising from the spire. Video showed that scaffolding around the base of the spire, part of extensive renovations that were underway, was one of the first places to visibly catch fire.
Some of the cathedral’s art may have been saved because of recent renovations. Last week, for instance, 16 copper statues representing the Twelve Apostles and four evangelists were removed with a crane so that the spire could be renovated.
Firefighters were able to save some of the cathedral’s artworks, including linen fabric associated with Saint Louis, the crown of thorns and the cathedral’s treasury, according to Monsignor Chauvet.