PARIS -- It started at 6:50 p.m. Paris time, just five minutes after Notre Dame Cathedral closed for the day. Within a matter of minutes, thick smoke and flames were leaping into the sky.
An hour into the blaze, the cathedral's iconic spire toppled.
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And it was all captured in real-time on social media by hundreds of horrified Parisians and tourists.
Watch the video above for a look at the most compelling videos. We've put them in sequential order, from the time they were posted on social media, to create a complete picture of how quickly the fire spread through the iconic building.