Diamonds worth millions stolen in Belgium Heist ... the Helvetic Airways aircraft from which millions' of dollars worth of diamonds were stolen. Belgian police are looking for eight men who made a hole in a security fence of Brussels international airport, drove onto the tarmac and stole diamonds worth tens of millions of dollars from the hold of a Swiss-bound plane. Anja Bijnens, a spokeswoman for the Brussels prosecutor, said the armed men, wearing masks, used two vehicles in their daring raid on Monday. Police found a burnt-out vehicle close to the airport later on Monday night but said they were still looking for clues. The diamond heist was estimated at about $US50 million ($A48.8 million), said Caroline De Wolf of the Antwerp World Diamond Centre. "What we are talking about is obviously a gigantic sum," De Wolf told VRT network. An airport spokesman says the robbers made a hole in the perimeter fence and drove up to the Swiss passenger plane that was ready to leave. The robbers got out of the car, flashed their weapons and took the loot from the hold, airport spokesman Jan Van Der Crujsse said. Without firing a shot they drove off through the same hole in the fence, completing the spectacular theft within minutes, he said. Van Der Crujsse was unable to explain how the area could be so vulnerable to theft. "We abide by the most stringent rules," he said. The Swiss flight, operated by Helvetic Airways, was cancelled after the robbery. Swiss, an affiliate of Germany's Deutsche Lufthansa AG, declined to comment on the heist, citing the ongoing investigation. The insurance for air transport - handled sometimes by airlines themselves or external insurance companies - is usually relatively cheap because it's considered to be the safest way of transporting small high value items, logistics experts say. Unlike a car or a truck, an airplane cannot be attacked by robbers once it's one its way, and is considered to be very safe before the departure and after the plane's arrival because the aircraft is always within the confines of an airport - which are normally highly secured.