Unknown perpétrations vandalised around 20 graves at a historic Jewish cemetery in the central Polish city of Lodz, police said Tuesday.
"The case is under investigation," Lodz police press officer Adam Kolas told PAP news agency.
The vandalism is believed to have occurred overnight Sunday to Monday.
Jewish community leaders in Lodz said that most tombstones, many toppled and now broken in half, had recently been renovated by relatives living abroad.
Poland's third largest city, Lodz was a major hub for the textile industry prior to World War II. Around a third of its residents were Jewish.
Nazi Germany set up the Lodz ghetto -- the Litzmannstadt ghetto in German -- in 1940, enclosing there around 220,000 Jews from occupied Poland and other European countries including Austria, Germany and the former Czechoslovakia.
It was the first ghetto created by the Nazis in occupied Poland and the last to be liquidated. Only the infamous Warsaw ghetto was larger.
Used primarily as forced labourers for Nazi Germany, some 50,000 Jews died there of exhaustion, hunger and disease inside an area of just four square kilometres (1.5 square miles).
Other ghetto residents were sent to their deaths in the gas chambers of the Auschwitz-Birkenau and Kulmhof am Ner concentration camps.
Only 830 people survived the Lodz ghetto's liquidation in August 1944.