Paris Mayor Anne Hidalgo said firefighters are trying to contain a "terrible fire" at the city's Notre Cathedral.
An AP reporter at the scene of Monday's fire said the roof at the back of the cathedral, behind the nave, is in flames and yellow-brown smoke and ash fill the sky.
Hidalgo urged residents of the French capital to stay away from the security perimeter around the Gothic-style church. The mayor says city officials are in touch with Roman Catholic diocese in Paris.