Police say some 20,000 people have turned out for Switzerland's biggest anti-nuclear power demonstration in a generation.
Demonstrators marched peacefully Sunday near the Beznau nuclear power plant in the northern canton (state) of Aargau. Beznau started operating 40 years ago and is Switzerland's oldest nuclear plant.
The last such major Swiss demonstration drew 18,000 people in 1986 against the Goesgen nuclear power plant in the northern canton of Solothurn.
Protest spokeswoman Michaela Loetscher said the unfolding disaster at Japan's Fukushima Dai-ichi nuclear plant, which was crippled by a March 11 tsunami, "has entirely changed the energy debate" in Switzerland.
Switzerland has five nuclear power plants that supply about two-fifths of its energy needs.