Investigators are unable to go inside Notre-Dame de Paris because the structure is unstable.
The Paris prosecutor said the devastating fire did not appear to be intentional, but investigators were limited by the safety risk.
"Right now the structure is not stable and we need to wait," the official said.
One firefighter was seriously injured battling Monday's blaze, but no other injuries or fatalities were reported.
Breaking: Paris prosecutor says structure of Notre Dame not stable, per @RichardEngel https://t.co/gbtiHNh7C3— Morning Joe (@Morning Joe) 1555410235.0