At least 42 people have died in Germany and dozens were missing on Thursday as swollen rivers caused by record rainfall across western Europe swept through towns and villages, leaving cars upended, houses destroyed and people stranded on rooftops.

As the water started to recede, stunned residents in the worst affected towns inspected what was left of their homes and neighbourhoods.

In the town of Schuld, houses were reduced to piles of debris and broken beams. Roads were blocked by wreckage and fallen trees and fish flapped and gasped on puddles of water in the middle of the street.

"We have had two or three days of constant rain. Or maybe four, I lost track," said Klaus Radermacher, who has been living in Schuld for 60 years.

"I saw the pizza store getting flooded, half an hour later the bakery was flooded. There is a camping ground up there, so caravans and campervans came floating past, gas tanks. We were powerless against it. It came so fast, I've never seen anything like it."

Eighteen people died and dozens were unaccounted for around the wine-growing region of Ahrweiler, in Rhineland-Palatinate state, police said, after the Ahr river that flows into the Rhine broke its banks and brought down half a dozen houses.

Another 15 people died in the Euskirchen region south of the city of Bonn, authorities said. People in the region were asked to evacuate their homes and emergency workers were pumping water from a dam south of Euskirchen town, fearing it could burst.

In Belgium, two men died due to the torrential rain and a 15-year-old girl was missing after being swept away by an overflowing river.

Hundreds of soldiers and 2,500 relief workers were helping police with rescue efforts in Germany. Tanks were deployed to clear roads of landslides and fallen trees and helicopters winched those stranded on rooftops to safety.

Around 200,000 households lost power due to the floods.

'Nature hitting out'

In Ahrweiler, two wrecked cars were propped steeply against either side of the town's stone gate and locals used snow shovels and brooms to sweep mud from their homes and shops after the floodwaters receded.

"I was totally surprised. I had thought that water would come in here one day, but nothing like this," said resident Michael Ahrend. "This isn't a war - it's simply nature hitting out. Finally, we should start paying attention to it."

The floods have caused Germany's worst mass loss of life in years. Flooding in 2002 killed 21 people in eastern Germany and more than 100 across the wider central European region.

Chancellor Angela Merkel expressed her dismay and vowed to help the affected communities rebuild.

"I tell those affected: we will not leave you alone in those difficult and scary times," she said during a news conference at the White House alongside U.S. President Joe Biden, who expressed his condolences to the victims. "We will also help with reconstruction."

In Washington for a farewell visit before she steps down following a federal election in September, Merkel said weather extremes were becoming more frequent which required action to counter global warming.

Pope Francis also extended his condolences to the victims and their families.

Armin Laschet, the conservative candidate to succeed Merkel as chancellor and premier of the hard-hit state of North Rhine-Westphalia, blamed the extreme weather on global warming.

"We will be faced with such events over and over, and that means we need to speed up climate protection measures, on European, federal and global levels, because climate change isn't confined to one state," he said during a visit to the area.

Climate and the environment are central themes in the election campaign, in which Laschet is going head-to-head with Social Democrat candidate Olaf Scholz and Annalena Baerbock of the Greens.

Power outage

In Belgium, around 10 houses collapsed in Pepinster after the river Vesdre flooded the eastern town and residents were evacuated from more than 1,000 homes.

The rain also caused severe disruption to public transport, with high-speed Thalys train services to Germany cancelled. Traffic on the river Meuse is also suspended as the major Belgian waterway threatened to breach its banks.

Downstream in the Netherlands, flooding rivers damaged many houses in the southern province of Limburg, where several care homes were evacuated.

In addition to the fatalities in the Euskirchen region, another nine people, including two firefighters, died elsewhere in North Rhine-Westphalia.

Further down the Rhine river, the heaviest rainfall ever measured over 24 hours caused flooding in cities including Cologne and Hagen, while in Leverkusen 400 people had to be evacuated from a hospital.

In Wuppertal, known for its overhead railway, locals said their cellars had been flooded and power cut off. "I can't even guess at how much the damage will be," said Karl-Heinz Sammann, owner of the Kitchen Club discotheque.

Weather experts said that rain in the region over the past 24 hours had been unprecedented, as a near-stationary low-pressure weather system also caused sustained local downpours to the west in France, Belgium and the Netherlands.