Lilli Hollein, MAK general director, said “the theft of a highly valuable piece of jewellery… has hit us hard”.
She said in a statement that MAK had developed a security plan with Van Cleef & Arpels specifically for the exhibition, adding: “Security issues were taken very seriously and all security measures were carefully prepared.”
Hollein said staff had reacted calmly and followed the established procedures when the “armed incident” occurred, and that no one had been injured.
She added that MAK had thoroughly reviewed its security measures ahead of the exhibition, “particularly in light of the incidents at major museums in recent years”.
Also on Thursday was one of the most important troves of prehistoric jewellery and artefacts was stolen from a Spanish museum.
Four Renaissance paintings were stolen from a museum in Sicily earlier this month, while three paintings by Renoir, Cézanne and Matisse worth millions of euros were taken from a museum in Parma earlier in the year.
These heists came after the brazen daylight raid on the Louvre in Paris, in which a masked gang stole priceless jewels last October.