Laurent Nuñez praised the "courage and determination" of firefighters who "risked their own lives" to salvage the building's stone structure and its two towers.
The fire ravaged the cathedral's roof and caused its spire to collapse.
French President Emmanuel Macron has vowed to rebuild it within five years.
The cause of the blaze is unclear.
"We now know it all came down to 15-30 minutes," Mr Nuñez said, adding that police and fire services would spend the next 48 hours assessing the security and safety of the structure.