A firefighter has explained how the roof of Notre Dame Cathedral has been "surrendered" in a bid to save the walls.
US firefighter Gregg Favre, a former St Louis firefighter, who was deputy director of the Missouri department of safety, likened the images of Notre Dame to a 2016 fire which destroyed the Orthodox Cathedral of St Sava Fire in New York City.
In a Twitter thread which went viral he explained how the church's heavy timber construction was problematic due to its large open spaces and fire stops.
"A firestop is a passive fire protection system made up of various components and used to seal openings in buildings," he wrote.
"If the fire started high on the structure, there is a chance that Paris Fire can save the walls and unimpinged areas of the Cathedral.
"But the roof has basically been surrendered at this point. The peak, the lack of access and fire spread means almost certain loss."