Authorities in the Mekong Delta's Bac Lieu Province have discovered 35 bombs left over from the Vietnam War-- ten of them were found in construction material storehouses.
The unexploded ordnance are all still equipped with active fuses.
One 250kg bomb was found on the premises of construction material retailer while workers were gathering sand using heavy machinery.
Bac Lieu military officials said the bombs were designed in the US to cause heavy damage.
The officials said the bomb must have been taken from the Hau River in Can Tho when barges often dredge for sand. The bomb was not discovered until its arrival in Bac Lieu.
At least three similar bombs were found at local sand stores this month, officials said.
Commander Ho Van Dai of the Bac Lieu Military Command said the number of bombs entering the province has increased fivefold over last year.
Cmdr. Dai only expects the number to rise as barges continue to collect sand in the Hau River, where US bombing was very heavy.