Burglars have stolen three diamond jewellery sets from one of Europe’s largest treasure collections – the Dresden Green Vault in eastern Germany.
The sets consist of 37 parts each, and the thieves may try to break them up.
Dresden police and museum officials say they are still trying to establish exactly how much was stolen in the break-in early on Monday.
Saxony’s ruler, August the Strong, created the collection in the 18th Century.
“Three out of 10 diamond sets have gone,” said Marion Ackermann, head of the Dresden state museums.
The 18th-Century sets are reported to also include some rubies, emeralds and sapphires.
Dozens of police cars are at the scene and the Green Vault is now shut. The thieves – still on the run – got in by removing part of an iron grille on a ground-floor window, then smashing the glass.
Ms Ackermann described the jewels as “priceless – we can’t put a figure on it”.
Earlier, the popular German daily Bild said the thieves had grabbed jewels worth one billion euros.
“The items cannot be sold on the art market legally – they’re too well known,” said Ms Ackermann.
Police are examining CCTV footage, which shows two suspects in the dark. But there could have been more involved in the robbery.
It is called the Green Vault because some rooms were decorated with malachite-green paint. It is housed in the Residenzschloss – a former royal palace.
At about 05:00 (04:00 GMT) on Monday, firefighters were called to tackle a fire at a nearby power distributor. There is speculation that the fire disabled the museum’s alarm system.
The most valuable items are in the palace’s historic section on the ground floor.
Police say a car found to be burning in Dresden early on Monday may have been the getaway vehicle set ablaze by the burglars.
The treasures include a figure of a moor studded with emeralds and a 648-carat sapphire – a royal gift from Russia’s Tsar Peter the Great.
Saxony’s minister-president, Michael Kretschmer, voiced outrage at the crime, saying “not only were the state art collections burgled, but the people of Saxony too”.
“The valuables housed in the Green Vault and Residenzschloss were acquired by people in the Saxony Free State with difficulty, over many centuries.” He said the collection was an integral part of Saxony’s history.