Thieves stole jewelry and other treasures worth up to one billion euros from a museum in eastern Germany in the early hours of Monday, the Bild newspaper reported.
The thieves cut off power to the Green Cellar Museum, home to one of Europe's largest collections, the newspaper said, without giving a source.
Police closed the building in the heart of the old city of Dresden and said they were still trying to count the loot. "We have not identified the perpetrator yet and we have not arrested anyone," police spokesman Marco Laski said.
Museum staff have yet to comment.
Augustus the Strong, one of the princes of Saxony and later King of Poland, founded the museum's collection in the 18th century.
One of the most famous treasures of the museum is a green diamond weighing 41 carats but was seconded to the Metropolitan Museum of Art in New York at the time of the attack on the museum.
The holdings of the Green Cellar Museum survived the Allied bombing of World War II and were confiscated by the Soviet Union as spoils of war. But it was returned to Dresden, the historic capital of Saxony in 1958.
State Prime Minister Michael Kretschmer said the theft was a blow to the entire state.