A large proportion of Kalisz' Jewish population, which was about 20,000, fled during the time of the military campaign. Germans occupied the city on September 6. They immediately began brutal measures against the Jews: murder, robbery, humiliations, and other abuse. Later Jews were relocated to a central location, and in late 1939, thousands were sent to other cities, including Lublin. Of the remaining, in October 1940, hundreds were murdered in a nearby forest. In 1941, about 100 were sent to Poznan for forced labor and more than 200 were murdered, some in gas vans. In 1942, the remaining Jews were sent to Poznan and to the Lodz ghetto.