Holocaust: Nazis Built 42,500 Camps, Study Finds

New research has discovered the Nazis created more than six times the number of concentration camps as previously thought and may have killed or imprisoned up to 20 million people.

Some 42,500 Nazi ghettos and camps have been catalogued by researchers at the US Holocaust Memorial Museum after 13 years of analysis.

That number includes "killing centres", forced labour camps, prisoner-of-war camps, "care" centres where pregnant women were forced to have abortions or their babies were killed after birth and brothels, The New York Times reported.

At the start of the project in 2000, the researchers had expected to find around 7,000 Nazi facilities across Europe.

Hartmut Berghoff, director of the German Historical Institute in Washington, told the newspaper: "The numbers are so much higher than what we originally thought.

"We knew before how horrible life in the camps and ghettos was, but the numbers are unbelievable."

Among that figure were 30,000 slave labour camps; 1,150 Jewish ghettos; 980 concentration camps; 1,000 prisoner-of-war camps; 500 brothels and thousands of other camps where elderly people were euthanised or forced abortions carried out.

The construction of the camps began as early as 1933 with the imprisonment of political opponents to Adolf Hitler, but they were also used to imprison gypsies and many other ethnic groups as Germany began to invade Europe.

The largest of the camps - the notorious Warsaw Ghetto - held around 500,000 people.

During the Holocaust, the Nazis were thought to have killed six million Jewish people in Europe.

Survivors could use the research with claims over unpaid insurance policies and looted property claims.