Mrs Merkel visited affected areas of western Germany on Sunday, talking to survivors and emergency workers. At least 188 people in Germany and Belgium are now known to have died in the floods. Heavy rain is continuing to wreak havoc, with attention now shifting to parts of Austria and southern Germany.
Emergency crews rescued people from homes in the Austrian region of Salzburg, where floodwaters submerged the streets of one town. The fire brigade said the capital Vienna saw more rainfall in an hour on Saturday night than in the previous seven weeks. In the Upper Bavaria region, one person was killed as heavy rains deluged basements and roads.
Meanwhile in western Germany, authorities said the Steinbachtal dam, south-west of Bonn, remained at risk of breaching after residents were evacuated from homes downstream.
European leaders have blamed climate change for the floods, which have also affected Switzerland, Luxembourg and the Netherlands. Experts say global warming makes torrential rainfall more likely. The world has already warmed by about 1.2C since the industrial era began.
Mrs Merkel said the world had to "be faster in the battle against climate change".
She walked through the badly-hit village of Schuld, surveying the damage and speaking to residents and emergency workers. Later she pledged to fast-track aid for reconstruction. "We are by your side," she said, describing the situation as "terrifying". "It is shocking - I can almost say that the German language doesn't have words for the destruction that's been wreaked," she said.
Finance Minister Olaf Scholz said a package of €300m ($354m; £257m) in immediate aid would be proposed at a cabinet meeting on Wednesday.
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