The identification of the bodies of victims who perished in a bar fire in Switzerland is a "nightmare" for forensic officials, a doctor told Reuters on Friday (January 2).

Investigators set about the painful task on Friday of identifying the burned bodies from a blaze that engulfed a crowded bar and killed around 40 people at a New Year's Eve party in the Swiss ski resort of Crans-Montana.

So severe were the burns suffered by the mostly young crowd of revellers in the Le Constellation bar that Swiss officials said it could take days before they name all those killed in the fire that also injured well over 100 people.

"This is a place that welcomes the public and a public that is not registered, so their identities were not taken at the entrance, there is no list, there are no elements," Bernard Marc, the head of forensic medicine at a French forensic unit in Compiegne said.

"Needless to say that their papers or any element of this type were burned in the fire or were destroyed by the water... There were many responders, who fortunately responded for rescue, but who modified this scene. So this is a bit of a nightmare,” he added.

Marc said that with many identifying features, such as the hands for fingerprints, the face and skin colour, destroyed by the blaze, authorities will most likely have to count on DNA comparisons and 3D imagery to try to identify the victims.

He said the identification process could take one week.

Production: Ardee Napolitano, Nicolas Coupe/Reuters