A guide and two mountaineering skiers died while another was seriously injured when snow gave way in the Mase-Val d’Hérens region, Valais cantonal police said.
The incident occurred around 2.40pm near the peak of the Pointe de Masserey at an altitude of 2,400 metres, police said.
The victims were part of a group of six, accompanied by the guide, who were descending after reaching the summit, according to a news release.
The three others were able to alert emergency rescue officials.
Five helicopters from Air-Glaciers and a rescue team of 26 people, including six doctors, and a canine squad responded to the call for help.
The four victims were transported to hospital but three of them died early in the evening, police said.
Identification of the dead remains under way and an investigation has been launched.
Earlier in the day, a 34-year-old man from the canton of Vaud died in an avalanche at the Nendaz ski area, part of the Quatre Vallées network of lifts that links with Verbier.
The snow slide was triggered by other skiers at around 11am, according to officials.
It occurred five minutes after a woman skier was carried away by another avalanche at Nendaz.
She was rescued and airlifted to hospital in Sion by an Air-Glaciers helicopter.
Meanwhile, a man was slightly injured by a snow slide on Sunday afternoon at the Nax-Mont Noble ski resort, near Sion.
Police noted that all of the avalanches happened in off-piste areas where conditions remain dangerous throughout the canton of Valais.
At least 11 people have died in avalanches in the Swiss Alps in less than two weeks.
Experts from the Institute for Snow and Avalanche Research SLF warned late last week of treacherous conditions in the Swiss mountains, particularly on north-facing slopes.
Snow from Christmas was resting on very weak old snow, meaning that in certain locations the weight of a single skier could make the snow cover collapse “like a house of cards”.
Extreme skier Julien Lopez was to lucky to survive an avalanche in the Val Ferret region of Valais last April.
A YouTube video of his experience graphically highlights the risks: