Berlin: Thieves have broken into Dresden's Green Vault, at one of the world's oldest museums, making off with three "priceless" sets of 18th century jewellery that German officials said would be impossible to sell on the open market.

The treasury of Augustus the Strong of Saxony was established in 1723 and today contains around 4000 objects of gold, precious stones and other materials on display in Dresden's Royal Palace.

Part of the White Silver Room collection inside Dresden's Green Vault. Credit:AP

Authorities said it appeared the thieves had broken open only one glass case containing three sets of Baroque jewellery made up of dozens of gems each.

"This is a bitter day for the cultural heritage of Saxony," state's Interior Minister Roland Woeller said.