A video that showed bystanders in Paris singing “Ave Maria” while watching helplessly as Notre Dame Cathedral was engulfed in flames was viewed over three million times on Twitter, reports said.

James McAuley, the Paris correspondent for the Washington Post, recalled watching the Parisians come together trying to grasp what was occurring.

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“All of us who’ve reported in Paris recently have known many tragic nights in this most beautiful of cities,” he tweeted. “But tonight is different. Impossible to describe the bewilderment, the eerie quiet, the tears at the sight of 800 years of history vanishing in less than hour.”

Investigators are treating the fire that engulfed Paris' Notre Dame Cathedral as an accident for now, the local prosecutor's office said Monday evening.

Paris police will investigate the disaster as "involuntary destruction caused by fire" and have ruled out arson and potential terror-related motives for starting the blaze, officials said.

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Fire chief Jean-Claude Gallet confirmed that firefighters had managed to stop the fire spreading to the northern belfry, the stomping ground of the fictional hunchback Quasimodo in Victor Hugo's 1831 novel "The Hunchback of Notre Dame." He added that two-thirds of the cathedral's roof "has been ravaged" and confirmed that one firefighter was injured, the only known injury from the fire.

Fox News' Samuel Chamberlain contributed to this report