Chancellery of President of the Republic of Poland Andrzej Duda wrote on Twitter:
In connection with the deaths of 12 Poles who died as a result of Thursday’s methane explosion at the ČSM hard-coal mine in Karviná, in the Czech part of the Cieszyn Silesia region, Sunday will be a day of national mourning throughout Poland.
As reported on the RMF FM radio website:
During national mourning, national flags on public buildings are lowered to half-mast and draped with black ribbons; mass, entertainment, concert and sporting events are cancelled.
Details are available on the rmf24.pl website.