Paris public prosecutor Remy Heitz said there was no obvious indication the fire was arson. Fifty people were working on what would be a long and complex investigation. One firefighter was injured but no one else was hurt in the blaze which began after the building was closed to the public for the evening…

Investigators will not be able to enter the cathedral’s blackened nave until experts are satisfied its stone walls withstood the heat and the building is structurally sound.

“Our job today is to monitor the structure and its movements,” said fire service spokesman Gabriel Plus.