BERLIN—At least six people have died and several people are missing in Germany after heavy flooding turned streams and streets into raging torrents, sweeping away cars and causing some buildings to collapse. Police in the western city of Koblenz said in a tweet Thursday that four people had died in Ahrweiler county, and about 50 were trapped on the roofs of their houses awaiting rescue. Six houses had collapsed overnight in the village of Schuld. “Many people have been reported missing to us,” police said. Authorities have declared an emergency in the region after days of heavy rainfall. Large parts of western and central Germany, as well as neighboring countries have experienced widespread damage. Police said an 82-year-old man died after a fall in his flooded basement in the western city of Wuppertal, which was among the hardest-hit. A fireman drowned Wednesday during rescue work in the western German town …