The city was occupied by Germany following the German–Soviet invasion of Poland, which started World War II in September 1939. On 14 December 1939, the Germans murdered 46 Poles from Pruszków during the large Palmiry massacre. Before the invasion, the city had a large Jewish population. In 1940, the German occupation authorities established a Jewish ghetto in Pruszków, in order to confine its Jewish population for the purpose of persecution and exploitation. The ghetto was liquidated on 31 January 1941, when all its 1,400–3,000 inhabitants were transported in cattle trucks to Warsaw Ghetto, the largest ghetto in all of Nazi occupied Europe with over 400,000 Jews crammed into an area of . From there, most victims were sent to Treblinka extermination camp.