At least 67 people have died in Germany and Belgium after record rainfall caused rivers to burst their banks.
Most of the victims were in Germany, but nine died in Belgium, including a 15-year-old girl.
The German states of Rhineland-Palatinate and North Rhine-Westphalia were worst hit, but the Netherlands is also badly affected.
More heavy rain is forecast across the region on Friday, while local officials have blamed climate change.
Armin Laschet, the premier of North Rhine-Westphalia, blamed the extreme weather on global warming during a visit to a hard-hit area.
“We will be faced with such events over and over, and that means we need to speed up climate protection measures… because climate change isn’t confined to one state,” he said.
Experts say that climate change is expected to increase the frequency of extreme weather events, but linking any single event to global warming is complicated.
German Chancellor Angela Merkel, who is in the US ahead of a meeting with President Joe Biden, called the flooding a “catastrophe” and said she was “grieving those who have lost their lives”.
“My thoughts are with you, and you can trust that all forces of our government – federal, regional and community – collectively will do everything under the most difficult conditions to save lives, alleviate dangers and to relieve distress.”
In Germany, police helicopters and hundreds of soldiers have been deployed to affected areas to help stranded residents.
Dozens of people waited on rooftops to be rescued.
Schools have been closed around the west of Germany, while transport links have been severely disrupted.
About 25 houses are in danger of collapsing in the district of Schuld bei Adenau in the mountainous Eifel region, where a state of emergency has been declared, according to German broadcaster SWR.
It said some houses had been completely cut-off and could no longer be reached by boat.