A shell or grenade has exploded, killing two people.

“It’s a shell that exploded with four workers there, a conventional device from World War I. One died instantly, another on the way to the hospital,” Ypres police chief Georges Aeck said, adding that another worker was in a critical state and the fourth in shock.

It was buried in western Belgium since World War One. At least two more were injured, one of whom is in critical condition.

The device was set off as workmen at a building site in Ypres were trying to dig it up.

A strategic city, Ypres was shelled by German forces for most of the war and unexploded weapons are often found there.