Four people died and about 20 were injured in an apartment building collapse in Poznan, western Poland, most likely to have been caused by a gas explosion, state-run news agency PAP said on Sunday.

The explosion on Sunday morning destroyed four of 18 apartments in the building, PAP said, quoting a local fire brigade representative.

The prosecutor¡¯s office said an investigation is expected to start on Monday.

¡°Looking at the degree of destruction of this building, it was initially assumed that it could have been a gas explosion, but we do not have certainty yet. For now, our activities are focused on the rescue operation,¡± a state fire service spkesman told broadcaster TVN24. Many households in Poland use gas for cooking or heating water.