The levels of many Swiss lakes and rivers rose to critical levels on Thursday after torrential rain hit many parts of the country.
Thousands of policemen, firemen, civil defence workers and soldiers are in action to pump water out of flooded cellars and clear roads as the rain continues.
The situation has led to chaos on the roads, with many closed as a result of flooding or landslides. Rail traffic was also hit.
Sirens sounded the alarm in several parts of the country on both Wednesday evening and Thursday, and hundreds of people were evacuated from their homes.
One man was seriously injured by an uprooted tree in Littau near Lucerne. A fireman was admitted to hospital in Bern, and another was in a Fribourg hospital after suffering from carbon monoxide poisoning.
In canton Bern, the water levels of the lakes of Thun, Brienz and Biel were just short of critical.
Residents of the Matte area of Bern were fighting the water of the River Aare with sandbags but several properties were already damaged.
The city's camping ground was evacuated and people were taken to safety at similar grounds in Brienz and Unterseen in the Bernese Oberland.
Animals at Bern's zoo, parts of which are located next to the River Aare, were also moved to safety, and several areas of the town were left without electricity.
Police in Solothurn have reported that the situation in the town of Olten, a strategic crossroads of Switzerland's rail network, was particularly precarious.
In Basel, the River Rhine is being monitored closely, with shipping at a halt for the time being.
In the neighbouring canton of Aargau the high water situation along the Aare was described as acute, with some areas under more water than in the flooding of 2005.
Elsewhere in the country, the town of Delémont - capital of canton Jura - was cut off, with roads closed and rail links cut.
In the commune of Villeneuve in canton Vaud some 50 people were evacuated from three camping grounds and houses.
The Swiss Federal Railways was urging people to seek information about the situation in their region before travelling.
The regions where rail transport was worst affected by flooding were northwestern Switzerland, the central plateau and Winterthur, north of Zurich.
The line between Bern and Fribourg was closed, with buses replacing the train service.
MeteoSwiss, the national weather service, warned that rain would continue to fall across much of the country throughout Thursday, although it believed the worst was now over.
It noted that Zurich had experienced its worst rainfall in a century, with 100 litres per square metre falling in 24 hours between Wednesday and Thursday.
MeteoSwiss said 74 litres of rain per square metre had fallen on Bern in the same period.
Other badly affected areas were the Chasseral in canton Bern (90 litres), the Moléson in canton Fribourg (80 litres) and Lugano (70 litres).
MeteoSwiss pointed out that the present rainfall had not overtaken the record amounts that caused chaos in Switzerland in August 2005.
Between 200 and 300 litres had fallen locally in 24 hours during the most critical period then.
swissinfo with agencies
Rainfall and flooding chronology
June 8, 2007: Three people died in flooding in Huttwil and Eriswil (canton Bern).
August 21-23, 2005: Eight people died after heavy rainfall and flooding in Bern and east and central Switzerland. Many road and rail connections were cut, with the villages of Engelberg and Lauterbrunnen cut off. The damage came to SFr2.5 billion.
October 14/15, 2000: Persistent rain in canton Valais led to landslides and flooding. Sixteen people died, including 13 in the village of Gondo. The bill came to SFr500 million.
May 15, 1999: Damage estimated at SFr580 million was caused after storms in several regions, including Bern, Thun, Rheinfelden and Lake Constance.
August 15, 1997: Storms with landslides caused damage of SFr120 million in Sachseln, canton Obwalden.
September 24, 1993: After heavy rainfall, the River Saltina burst its banks, causing severe damage in the town of Brig. Two people died, with damage estimated at SFr600 million.
Summer 1987: Eight people died after storms in Poschivao and the Reuss plain in canton Uri. Damage totalled SFr1.3 billion ($1.09 billion).
The Swiss Solidarity Foundation, has issued a reminder that it already has a fund-raising campaign after the June floods in Switzerland, which affected the Emmental and Entlebuch regions as well as parts of canton Schwyz.
The foundation led by swissinfo's parent body, the Swiss Broadcasting Corporation, said the account for donations was Swiss Solidarity 10-15000-6 "Natural Disaster Switzerland".
Together with partner organisations Caritas (Catholic charity) and the Swiss Red Cross, Swiss Solidarity provides fast and unbureaucratic aid in cases of hardship.
The Swiss Federal Railways is advising travellers to seek information about the current situation of the rail network and is warning of delays.
Information can be found on the internet at www.sbb.ch/166.
There is also a free telephone hotline: 0800 99 66 33
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