The posh ski resort of Davos was snow-bound Monday after the heaviest precipitation in two decades, hampering the arrival of the world's elite for this week's World Economic Forum (WEF).

"In the last six days, 159 centimetres (63 inches) of snow fell on Davos (...) a fall that we observe only every 20 years," Switzerland's Institute for the Study of Snow and Avalanches said in an evening bulletin.

"From Monday evening until the end of the snow overnight, an additional 20 to 40 cm will be added," the Institute said, evoking an "exceptional" situation.

Heavy snow has been blanketing Davos for days. After a brief lull Monday, large flakes began to fall in the early afternoon, disrupting traffic and threatening to block the landing of VIP helicopters.

An economist registered at the forum told AFP it took two hours to drive the last 12 kilometres (seven miles) approaching the resort.

Trains were more crowded with official Davos delegates, who usually take limousines and special shuttle vehicles to the week-long forum.

In the centre of Davos, participants preferred to walk rather than take the shuttles, which were slowed down by roads resembling skating rinks.

Cars and pedestrians intersected between high powder walls of snow. The streets are not salted in Davos, to protect the environment.

On Sunday, the snowfall had already disrupted the road traffic and temporarily cut the railway line leading to the ski resort.