Officers say they caught a businessman unloading the masks from a lorry into a house in St Denis, north of Paris.
Last month, France requisitioned all stocks and production of face masks to equip health workers.
Meanwhile in China, the authorities have confiscated 89m poor quality face masks. The country has faced criticism over poor quality exports.
Officials had inspected nearly 16 million businesses and had also seized large quantities of ineffective disinfectant, government official Gan Lin said.
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And in Germany, medical wholesalers say they have almost run out of masks. From Monday it will be compulsory for people to cover their faces in shops and on public transport in the country.