A diamond with a market value of 200 million yen ($1.8 million) was stolen from a convention facility in Yokohama, near Tokyo, police said Thursday.

The 50-carat loose diamond was on display as part of a jewelry exhibition at Pacifico Yokohama in the waterfront area of the city, according to the police.

They said an employee of the company providing the diamond noticed around 6 p.m. that the stone was missing, with its showcase apparently unlocked.

As the company said the diamond was in the showcase at around 5 p.m., the police believe it was stolen during the short period of time.