Harrowing new video has emerged showing flames spreading across the ceiling of a Swiss bar with young revellers losing crucial seconds by filming the blaze instead of fleeing.

The footage, taken by French economics student Ferdinand Du Beaudiez, shows flames ripping through the Crans-Montana club as revellers below continue singing, dancing and shouting, oblivious to the danger building above them.

The inferno killed at least 40 people and another 119 were injured, authorities confirmed today - most of them in their teens and twenties with severe third-degree burns. 

While Swiss authorities today said there were 40 victims, Italian authorities said 47 were dead.

Moments before the fire, a waitress had been seen dancing and waving a lit sparkler beneath foam soundproofing panels on the ceiling, which then caught light.

Several people can be seen holding up their phones as the fire grows overhead, apparently unaware they are capturing the moments before disaster strikes. 

Some can be seen frantically trying to extinguish the inferno, but within seconds it took hold, erupting into a deadly fireball that engulfs the packed bar.

As the horror unfolded, Ferdinand escaped - then made the extraordinary decision to go back inside.

The brave student has now told how he re-entered the burning Le Constellation basement bar twice in a desperate attempt to save his brother and girlfriend, trying to pull bodies from the flames as chaos and smoke filled the venue.

He told how he found a badly burned person lying on the stairs and couldn't even tell if it was a man or woman: 'Their clothes were burned, I could only make out teeth.'

He recalled: 'I tried to grab this person who was really heavy, but there was no tension in their arm. I just slid him on the ground, then the police and firemen took over from me.'

Images show the moment before a deadly New Year's Eve blaze a Swiss ski resort bar killed at least 40 people. A waitress had been seen dancing and waving a lit sparkler beneath foam soundproofing panels on the ceiling, which then caught light

 A dramatic video captured the moment the ceiling of a Swiss ski bar caught fire 

The footage, taken by French economics student Ferdinand Du Beaudiez, shows flames ripping through the Crans-Montana club as revellers continue singing, dancing and shouting - unaware they are already trapped in extreme danger

In the video footage someone can be seen trying desperately to extinguish the fire, but within seconds it takes hold, erupting into a deadly fireball that engulfs the packed bar

Beatrice Pilloud, Valais Canton attorney general, confirmed in a press conference today that the blaze was likely caused when sparklers in champagne bottles made the ceiling catch fire.

All bar six of the 119 injured have been formally identified, but the severity of the burn wounds means many survivors and victims are unrecognisable.