HONG KONG • Hong Kong police have defused a World War I hand grenade that was found hidden in a pile of potatoes at a potato chip factory owned by popular Japanese snack maker Calbee.

It was reported that a worker picked up the device, which was covered in a thick coat of dirt, among a batch of tubers during a potato-screening process early yesterday morning.

The undetonated weapon was taken to the security office and police were called in for help at the factory in Tseung Kwan O Industrial Estate, Hong Kong's Chinese-language newspaper Ming Pao reported.

The grenade was defused around three hours later by the bomb disposal squad about a metre underground within the plant compound.

Tseung Kwan O assistant district commander (operations), Mr Wong Ho Hon, told reporters the grenade weighed 1kg and measured 80mm in width.

He added that the German-made device was thrown during World War I but did not explode then.

Police have ruled out criminal activity as they believe the dirt-crusted grenade had ended up in Hong Kong in a shipment of potatoes from France.