Robbers stole three priceless diamond sets from a German state museum in Dresden, police and museum directors said, in what German media have described as the biggest art heist since World War II.

The thieves at dawn broke into the Green Vault at Dresden´s Royal Palace — home to around 4,000 precious objects of ivory, gold, silver and jewels after a power cut deactivated the alarm.

The stolen items included brilliant-cut diamonds that belonged to a collection of jewellery of 18th-century Saxony ruler Augustus the Strong.

Museum directors had earlier feared much of three sets of diamond jewellery in the collection were snatched, but the loss turned out to be more limited than thought.

“The criminals didn´t manage to take everything,” the director of Dresden´s state art collections Marion Ackermann told.

Nevertheless, the stolen items are of inestimable art-historical and cultural-historical value, she said.

“We cannot put an exact value on them because they are priceless,” said Ackermann, adding she was shocked by the brutality of the break-in.

The thieves launched their brazen raid after having set off a fire at an electrical panel near the museum in the early hours of Monday, deactivating its alarm as well as street lighting, police said.

Despite the power cut, a surveillance camera kept working and filmed two men breaking in.

A video released by police showed one of the men, armed with a torch, using an axe to smash the display case.

The suspects then fled in an Audi A6 and remain on the run.

The apparent getaway car was found on fire later elsewhere in the city, said police, adding that the vehicle was being examined for clues.