At least 120 people have died and hundreds more in western Europe are unaccounted for after some of the worst flooding in decades.
Record rainfall caused rivers to burst their banks, devastating the region.
In Germany, where the death toll now stands at over 100, Chancellor Angela Merkel called for a determined battle against climate change.
At least 20 people have died in Belgium. The Netherlands, Luxembourg and Switzerland are also affected.
Many factors contribute to flooding, but a warming atmosphere caused by climate change makes extreme rainfall more likely.
The world has already warmed by about 1.2C since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.
Belgian Prime Minister Alexander De Croo declared 20 July a national day of mourning.
"We are still waiting for the final toll, but this could be the most catastrophic flooding our country has ever seen," he said.
Scale of damage becoming clear
We met an elderly man trying to get into a village which was all but destroyed. His grandchildren were there, he said, but he couldn't get hold of their parents.
Even the authorities say they don't know for sure how many people are missing. There is no phone signal in much of the region, making communication all but impossible. But the death toll is expected to rise today and with every hour that passes the magnitude of this disaster becomes ever clearer.
All along the River Ahr there are flooded homes, broken bridges, the twisted remains of campsites and caravan parks. For many of the dazed people we met surveying the damage here, it's almost impossible to imagine clearing up and starting again.
Some 15,000 police, soldiers and emergency service workers have been deployed in Germany to help with the search and rescue.
Entire villages have been destroyed, and officials in the western German district of Ahrweiler say up to 1,300 people are unaccounted for.
Gregor Jericho, a resident of Rheinbach in North Rhine-Westphalia, told the BBC: "It's a very sad scene. Streets, bridges and some buildings are destroyed. There's garbage everywhere.
"Parts of buildings are in the road, people are sitting and crying. It's so sad. People have lost their homes, their cars are in fields flooded. My city looks like a battle has taken place."
In the same town, Ansgar Rehbein told Reuters he saw the river's water level rising so rapidly that he had to immediately get out of his house.
"Once the river started overflowing and the water came down from the hillside, it was a matter of two minutes before the courtyard was flooded with waist-high water," he told the news agency.
"We had to get out through the window and uphill in order to save ourselves."
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In Belgium, dramatic footage of the floods showed cars being swept away along a street in the city of Verviers. A curfew was in place overnight because of the risk of looting.
Residents of Liège, Belgium's third-largest urban area after Brussels and Antwerp, were ordered to evacuate on Thursday. Local officials said those unable to leave should move to the upper floors of their buildings.
The Meuse river, which flows through the city, stabilised on Friday morning, with small overflows in some areas.
Chronicle of a disaster foretold
Scientists have condemned politicians for failing to protect their citizens from extreme weather events such as the floods in northern Europe and the US heat dome.
They have been predicting for years that summer rainfall and heatwaves would become more intense due to human-induced climate change.
Hannah Cloke, Professor of Hydrology at the University of Reading, said: "The deaths and destruction across Europe as a result of flooding is a tragedy that should have been avoided.
"Forecasters issued alerts early in the week, and yet the warnings were not taken seriously enough and preparations were inadequate.
"The fact that other parts of the northern hemisphere are currently suffering record-breaking heatwaves and fires should serve as a reminder of just how much more dangerous our weather could become in an ever-warmer world."
Scientists say governments must both cut the CO2 emissions that are fuelling extreme events, AND prepare for more extreme weather.
Yet in the UK - hit by severe flooding on Monday - the government's advisory climate change committee recently told ministers the nation was even worse prepared for extreme weather than it was five years ago.
It said the government was keeping only a fifth of its pledges to cut emissions.
And only this week the UK government told people that they don't need to reduce flying because technology will solve the emissions problem - a notion that most experts consider a gamble.
The Netherlands has reported no casualties but thousands of people in towns and villages along the Meuse river have been urged to leave their houses quickly.
The river running through the Swiss capital Bern burst its banks, flowing at a record rate of 560 cubic metres a second on Friday.
Lake Lucerne is flooding into the town and people in Basel have been told to keep well away from the River Rhine. There is also the risk of mud and rock slides in the Alps as the flood waters run off.
How does climate change cause flooding?
- Global heating causes more water to evaporate, which leads to an increase in the amount of annual rain and snow
- At the same time, a warmer atmosphere means it can hold more moisture - which also increases the intensity of rainfall
- Rather than gently watering plants, this intense rainfall leads to flooding, like we're seeing in Northern Europe now
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