The owners of a Budapest apartment have discovered a huge trove of documents relating to the Hungarian Holocaust in a wall cavity.

The 6,300 papers are part of a 1944 census of Budapest's Jews that was carried out to lay the ground for their extermination.

The documents contain a building-by-building record of residents surveyed and whether or not they were Jewish.

Brigitte Berdefy, one of the owners of the apartment, said that a workman detected the presence of paper after sticking a screwdriver into a crack in a wall. After carefully removing some bricks, she lifted 135lb of documents out from behind the plaster.

Budapest city archives chief, Istvan Kenyeres, told AFP: "The content and scale of the finding is unprecedented.

"It helps to fill a huge gap in the history of the Holocaust in Budapest… Jewish people filled in the forms honestly. They refused to believe where this might end up."

The May 1944 Budapest census aimed to identify houses that could serve as holding locations for Jews before being moved to a walled ghetto in the city's seventh district.

After the census, around 200,000 Jews were moved into 2,000 selected buildings, "Yellow Star Houses", with the Star of David painted on the doors.