During the joint German–Soviet invasion of Poland, which started World War II, in September 1939, it was invaded by Germany, and the "Einsatzgruppe II" entered the town to commit various atrocities against the populace. The Germans robbed, conscripted labor, forced into a ghetto, and then murdered almost all of the town's Jewish population, about one-third of the total population. Most were deported to the Chełmno extermination camp where they were immediately gassed. Others were murdered in the town or at the Jewish cemetery. Only about 10 of Plaszka's pre-war Jewish population of around 1000 is thought to have survived the war. In 1943, the Germans expelled 252 Poles and deported them to forced labour to Germany. More than 30% of the town's population died. The German occupation ended in 1945.