Heavy rains are swelling rivers, closing roads and causing power cuts in cantons Ticino, Uri and Graubünden in the eastern parts of the country.
Forecasters say in Ticino over 300 mm of rain per square meter fell in 48 hours, the same amount expected in the whole of August.
The Rhine River is rising and has burst its banks in some areas and is flowing strongly through Chur.
Some paths, bridges and roads have been closed along the route.
Flood warnings are in place in canton Sankt Gallen.
The rain is expected to continue to around midday today.
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