Construction workers dug up around 900 artillery shells while building a local government office in the Mekong Delta province of Bac Lieu on Saturday.
The workers were driving concrete stakes to lay a foundation for the office of Phuoc Long District People's Committee in Phuoc Long Town when they discovered some artillery shells.
Local sappers were then called in to the 0.5-hectare construction site, where they unearthed around 900 artillery shells in three underground cellars.
Lieutenant-Colonel Ho Van Dai of the Bac Lieu Province Military Command said many of the 155-millimeter artilleries were still active. He said one round can kill people from up to 50 meters away.
The site was once a base camp for the US-backed South Vietnam military forces during the Vietnam War, he said.
Sappers have blocked off the area and are still working to defuse all the artillery.
In 2008, a mortar shell exploded after a truck operated by a construction company hoed up soil for a road project near the location. No casualties were reported.