French President Emmanuel Macron says Notre-Dame cathedral will be rebuilt "even more beautifully" - and that he wants the work done within five years.
A massive fire on Monday ravaged the 850-year-old Gothic building, destroying much of its roof and causing its steeple to collapse.
The cathedral was minutes away from total destruction, officials say.
But despite Mr Macron's pledge experts say its reconstruction could take decades.
Fifty people will investigate the cause of the fire. Paris public prosecutor Rémy Heitz said there was no obvious indication of arson and that the blaze was being treated as an accident.
A combined €800m ($902m; £692m) has already been pledged by a number of companies and business tycoons to help rebuild the Unesco World Heritage site.
What has Macron said?
In a televised address on Tuesday evening, President Macron suggested he wants it rebuilt by the time Paris hosts the Summer Olympics in 2024.
"We'll rebuild Notre-Dame even more beautifully and I want it to be completed in five years, we can do it," said Mr Macron, who had already pledged to launch an international fundraising scheme for the reconstruction.
"It's up to us to convert this disaster into an opportunity to come together... It's up to us to find the thread of our national project."
But Eric Fischer, head of the foundation in charge of restoring the 1,000-year-old Strasbourg cathedral, told AFP the Notre-Dame may take "decades" to rebuild.
Frédéric Létoffé, the head of the group of companies for the Restoration of Historic Monuments, put the timescale at between 10 and 15 years, warning substantial work would be needed to secure the site before restoration can begin.