In the western city of Poznań, part of the roof of a sports hall collapsed. Fire crews were called in to deal with flooding in five hospitals and a cathedral in the city.
Downpours turned many Poznań streets into fast moving streams.
In other parts of the country, winds uprooted trees and disrupted power supplies. Officials advised people to stay away from open spaces and not to shelter under trees.
There were no reports of serious injuries as a result of the storms, which came after several days of scorching temperatures.
(pk)
Source: PAP/Polish Radio