The munitions dated back to World War II, local media reported.
The explosion occurred in a forest near the town of Kuznia Raciborska, the military said. Two of the injured were flown to hospital in serious condition.
The troops were part of a parachute regiment stationed in the region.
According to police, they were tasked with dealing with old artillery shells discovered a few days earlier by people walking in the forest.
World War II shells and bombs are still often found in Poland which was invaded by Nazi Germany.
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