Health Minister Adam Niedzielski said the cases were detected in the densely populated southern coal-mining region of Silesia.
Stricter rules came into force in Poland on Thursday requiring everyone arriving from Brazil, India and South Africa to go into quarantine for seven days. After that time, they will have to show an all-clear COVID test result for the quarantine to be lifted.
The rules were toughened after two hotspots of the Indian variant of the coronavirus were found in Poland.
Amid a fall in infections, the government on Tuesday allowed shopping malls, DIY stores and museums to reopen. It plans to gradually ease a swathe of other lockdown rules this month.
Pupils are set return to on-site lessons by the end of May, while gyms will be allowed to open and restaurants will be able admit guests to half capacity.
Officials on Thursday reported 6,431 new coronavirus infections and 510 more deaths, bringing Poland's total number of cases during the pandemic to 2,818,378 and fatalities to 68,993.