An art collection of over 1,500 paintings seized by the Nazis has been found in Germany, thanks to a random customs check. The paintings had long been believed destroyed in a 1945 RAF raid.

Germany's Focus magazine broke the story about the discovery of the horde, which includes paintings by Picasso, Matisse, Renoir and Chagall.

The paintings were discovered behind a stack of tinned beans and fruit in the squalid flat of Cornelius Gurlitt in the Munich suburb of Schwabing.

The collection was discovered by chance in 2011 when customs ran a routine check on a train from Switzerland. Officials questioned Gurlitt and became suspicious because of his shifty demeanour.

They found that he was not registered with the police, tax authorities or social services, which is mandatory in Germany. He also drew no pension and had no health insurance.

"He was a man who didn't exist," said one official.

On issuing a search warrant for his flat, they discovered the art treasure trove behind piles of rotting food.

"This is a sensational find," said a spokesman for German Customs. "A true treasure trove. It is an incredible story.

"They are worth over a billion euros, we are told, but the real worth is inestimable. They are treasures," he added.

Gurlitt's father Hildebrand was an art historian when the Nazis came to power in 1933. He acquired hundreds of artworks sold for a pittance by Jews who were trying to escape the Nazi regime.

Focus magazine reports that investigators found a bank book owned by Cornelius Gurlitt with half a million euros, from the sale of some artworks.

Gurlitt faces jail for tax evasion and money laundering.

The hunt now starts for the rightful owners of the paintings. One of the possible recipients is Anne Sinclair, the wife of Dominique Strauss-Kahn. She is the granddaughter of Paul Rosenberg who is said to have given his paintings to Gurlitt in exchange for safe passage out of Germany.

Strauss-Kahn, the former head of the International Monetary Fund, is facing charges of pimping in a French court.