Thieves emptied 123 of 160 diamond vaults in the Antwerp Diamond Center in mid-February, in what appears to be the biggest diamond theft in the history of Antwerp, a major diamond-cutting center.

“We are certainly talking about many millions [of dollars],” the Associated Press was told by Youri Steverlynck, a spokesman for the Diamond High Council (HRD), which oversees and represents the Belgian diamond industry. Authorities said the loss would exceed a $4.5 million 1994 robbery of five ADC vaults, until now the largest such theft.

More than 50% of the world’s diamond production—including rough and polished, gem and industrial quality—passes through Antwerp. The ADC houses dozens of diamond and gem companies. Cutters and dealers traditionally store their wares in the maximum-security vaults of the ADC in the heart of the two-square-mile diamond district.

The district is the best-protected area in Belgium, and the ADC the most secure area within the district. “Security has always been our strong point,” the AP was told by Steverlynck, who feared the theft “will hurt Antwerp’s image” as a diamond-trading center.

There were no immediate signs of forced entry in the weekend break-in, leading authorities to suspect it was as an inside job. “Interrogations of people working at the Center are ongoing,” Nuyts said a few days after the theft.