The 16-day camp in the western Polish town of Opalenica began on Monday and runs until June 8.
Due to the coronavirus pandemic, the players will be separated from fans and the media throughout their stay in Opalenica, news outlets have reported.
Poland kick off their Euro 2020 group-stage campaign with a fixture against Slovakia at Krestovsky Stadium in the Russian city of St. Petersburg on June 14.
The Polish team will next take on Spain at Estadio La Cartuja in Sevilla on June 19 and then play Sweden in St. Petersburg four days later.
Ahead of the European tournament, Poland will play two friendlies on home turf at the start of next month, taking on Russia in Wrocław on June 1 and then Iceland in Poznań on June 8.
Manager Paulo Sousa last week released an initial list of 26 players called up for the championships.
Poland boss Paulo Sousa. Photo: PAP/Leszek Szymański
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Source: PAP