Paris Mayor Anne Hidalgo says firefighters are trying to contain a "terrible fire'' at the city's Notre Dame Cathedral.
An AP reporter at the scene of Monday's fire says 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.
The peak of the church is undergoing a 6 million-euro renovation project.
French media quoted the Paris fire brigade saying the fire is "potentially linked'' to the renovation work.