Thousands of people have fled the area surrounding an unexploded weapons stockpile near Vimy, France.

Neighbouring Vimy Ridge was the site of a historic Canadian victory during the First World War. French newspapers at the time hailed the breakthrough as 'The Easter Surprise.' Now the shells used in the battle have brought another Easter surprise - 84 years later.

An endless flow of fluorescent red rescue vehicles broke the calm in Vimy. Police knocked on all doors in a three kilometre radius around a stockpile of 170 tons of unexploded ordnance.

Evacuating a nearby hospital

Most of it contains lethal mustard gas, now an illegal weapon in war.

A report completed last week found leaks in the water-filled containers used to store the shells, the likes of which are found almost daily all over this region.

France's Interior Minister rushed to Vimy to explain why some 12,000 people had to leave overnight, for a week, and maybe longer.

"The prime minister has decided as a precautionary measure, and for people's safety, to ask those most as risk to leave," said Interior Minister Daniel Vaillant.

By Saturday morning, the town of Vimy, and smaller villages nearby, were reportedly empty.

A few angry locals told reporters they wouldn't answer when police knocked on their doors. They didn't understand why they weren't warned months in advance. And some farmers, worried about having to move their livestock, also threatened to stay.

But after riot police swept through the area, most people are thought to have gone, out of the reach any gas cloud or explosion.

Only 50 bomb disposal experts and firefighters wearing gas masks, like the soldiers four generations back, are in the danger zone.

The shells must be cooled down in refrigerator trucks and will be ferried in nightime convoys to a military base for disposal.