Numerous rocks became detached mid-morning from the mountainside above the left bank of the valley, Valais cantonal police said.
“A cloud of dust spread across the area,” police said, adding that no-one was injured.
Valais’s cantonal geologist flew over the region at the beginning of the afternoon and established that “several thousand cubic metres of rocks” came free from a slope.
Police said there was no danger for transportation routes, including a rail line and a cantonal road to the mountain resort town of Zermatt, or for residential areas.
Experts do not expect a major landslide but other rockfalls are not ruled out in the area, without posing a danger to infrastructure or human life.
All the same, surveillance of the area has been stepped up, police said.
In the spring of 1991, two major landslides from a cliff in the Randa area brought 30 million cubic metres of rock crashing through the valley that links Zermatt and Visp.
Apart from blocking transportation routes, the natural events dammed a water course that flooded part of the town of Randa.
There were no deaths but farm animals perished and farmhouses and holiday homes were destroyed, while it took nine months to completely clear up the devastation.