Flevoland province police said a bang was heard on Snijdershof Street in Lelystad. Officers are investigating the scene. 

According to the newspaper, an explosive device was thrown into the supermarket, causing a fire. 
This is another attack on a Polish store in the Netherlands. They previously occurred in December 2020 and early June this year in Aalsmeer, Heeswijk-Dinther, Beverwijk and Tilburg. 
Police had set up a special team to investigate whether the attacks were related. Four suspects were arrested in June and are in custody.