Robbers dressed as police and armed with machine guns have stolen 120 parcels of diamonds worth millions of dollars from the runway of Brussels Airport.
It is believed to be one of the biggest robberies the diamond industry has seen.
Two vehicles carrying eight men drove up to a van belonging to security firm Brinks.
The firm had just finished loading the diamonds into a Swiss passenger plane.
The men, who were masked but also wore police uniforms, did not fire a single shot and the entire robbery took less than five minutes.
They escaped and are now being hunted by police.
Prosecutors said they could not yet comment on how much the diamonds taken were worth or to whom they belonged.
Belgian state broadcaster VRT reported the total value was €350m.
A spokeswoman for the Antwerp Diamond Centre said the value may be closer to €37m.
"In any case it's one of the biggest robberies we've seen," she said.
Antwerp has been a leading diamond centre for centuries, with some eight in every ten rough diamonds, and five in every ten polished diamonds, passing through it.
Both vehicles sped off after the robbery and one was later found burnt just outside of Brussels.
The robbers got out of the car, flashed their weapons and took the diamonds from the hold, airport spokesman Jan Van Der Crujsse said.
Mr Van Der Crujsse could not explain how the area could be so vulnerable to theft. "We abide by the most stringent rules," he said.
The Swiss flight, bound for Zurich and operated by Helvetic Airways, was cancelled.
Swiss, an affiliate of Germany's Deutsche Lufthansa AG, has declined to comment on the robbery, citing the ongoing judicial investigation.