Feb 14 (Reuters) - PKO BP has appointed Szymon Midera as acting CEO, starting Feb. 15 at a supervisory board meeting held on Wednesday at which six management board members were dismissed, Poland's biggest bank said.

The appointment follows Dariusz Szwed's resignation which was announced last week and became effective on Wednesday.

Midera, who was at the helm of Bank Pocztowy for eight years until June 2016, will also be acting deputy CEO, alongside Maciej Cieslukowski and Marek Radzikowski.

PKO BP did not provide reasons for Szwed's resignation. It said its supervisory board adopted a resolution to start recruiting for the CEO and deputy CEOs roles.

Poland's new government has been seeking to restructure the boards of state-owned companies following its election victory last year.

At Wednesday's meeting, PKO BP's supervisory board dismissed Maciej Brzozowski, Marcin Eckert, Pawel Gruza, Wojciech Iwanicki, Andrzej Kopyrski and Artur Kurcweil from the management board.

State-owned refiner Orlen, the biggest company listed on the Warsaw Stock Exchange, has seen similar changes to its board.

(Reporting by Anna Maria Nowak; Editing by Mark Potter and Emelia Sithole-Matarise)