World Jewish Congress president Ronald Lauder has warned the Bern Art Museum in Switzerland that it could be subjected to an "avalanche" of lawsuits if it accepts the bequest of artworks from German collector Cornelius Gurliit whose father dealt with Nazi loot.

Gurlitt, who died in May at age 81, left his $1.4-billion trove of artworks to the Swiss museum. Lauder has stated that provenance must be estalbished before the artworks can be given to the museum.

"If this museum in Switzerland gets involved with this inheritance, it will open Pandora's box and unleash an avalanche of lawsuits - possibly from German museums, but certainly from the descendants of the Jewish owners," Lauder said.

"The people in Bern will harm themselves and their country if they take these paintings before their provenance is cleared up. They would become a museum of stolen art," warned Lauder.