The sunken barge was found off the coast of Russia's western Kaliningrad exclave, Maxim Vladimirov, deputy head of the fire department of the emergency situations ministry, told the RIA-Novosti news agency.
"Following the examination of the sunken German barge... the presence of explosives was confirmed. According to preliminary estimates, more than 10,000 war-era munitions are there," Vladimirov said.
The barge was found close to the town of Baltiisk 1.5 kilometres from shore, he said, adding that emergency services would begin demining the sunken ship this month in a process expected to last three years.
The announcement comes one day after a World War II-era bomb exploded in Göttingen, Germany, killing three members of a bomb disposal unit.
Russia's Kaliningrad exclave, which borders Poland and Lithuania, was part of Germany until 1945 when it was captured by the advancing Red Army at the close of World War II.
Its German population fled or was expelled by the Soviets and the exclave is currently home to a major Russian naval base.