French President Emmanuel Macron announced an investigation even before the fire was put out, and vowed to reconstruct the historic building. The cause of the fire is not known yet. The prosecution department has assigned 50 people on the job of investigation. Reportedly, workers were doing renovation inside till 6 pm.

Plumes of smoke could be seen billowing out of the 850-year-old church, a landmark in the centre of Paris, for miles. The fire reportedly started between 6 pm and 7 pm (18:43) (16:43 GMT). The blaze was brought under control after 15 hours; 400 firefighters were deployed. The flames coming out the back of the cathedral looked like a torch.

The wooden spire and the roof have collapsed. There were also invaluable pieces of art and artefacts inside, some of which were quickly removed. The cross and the altar remained untouched by the fire. This is due to the fact that gold melts only at 1064 deg C while wood burns at 400 deg C.

The crown of thorns believed to have been worn by Christ on way to crucifixion was reportedly salvaged.

Eyewitnesses said the two sections of the roof as well as the spire have entirely collapsed. Firefighters saved the bell towers. So also the rose windows.

It was at this Notre Dame cathedral where Napoleon had his coronation as emperor in 1804, and where John of Arc was beatified.

The ancient cathedral is a Unesco World Heritage site. It draws 13 million visitors a year. Notre Dame in English means "Our Lady." The construction of the cathedral began in 1163 and completed in 1345. Victor Hugo's 1831 novel 'The Hunchback of Notre-Dame' had portrayed the poor condition of the cathedral that started the renovation work. The book is a Disney film now.