An unexploded First World War hand grenade was found among a shipment of French potatoes when they were unloaded at a Hong Kong crisp factory.

The German grenade is believed to have been left in a trench during the war and accidentally gathered up with potatoes planted a century later in the former battlefield.

Hong Kong police safely detonated the grenade at the Calbee snacks factory. Superintendent Wilfred Wong Ho-hon said it “was in an unstable condition because it had been previously discharged but failed to detonate.”

A police video showed bomb disposal officers packing the 3-inch wide grenade in a drainage channel before exploding it. It weighed more than 2lbs.

“All the information to date suggested that the grenade was imported from France together with the other potatoes,” Superintendent Wong said.