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.