Thieves have stolen jewelry worth about $825,000 from the world’s biggest watch and jewelry fair in Basel, The Associated Press reports.

The robbery took place April 10, two days before the opening of BaselWorld, a spokesperson for the Swiss prosecutor’s office told the AP Saturday. The jewelry was taken when it was being brought to a stall in the exhibition hall for the fair.

The theft is likely to be the largest in the fair’s recent history, Baselworld spokesman Bernhard Keller told the AP. But he said that security at the fair was adequate.

JCK