A city guard, left, and a rescuer walk with a little dog saved from the rubble of an apartment block that collapsed killing several people in the western city of Poznan, Poland. AP Photo

Moscow - A gas explosion in the western Polish city of Poznan that left five people dead may have been ignited on purpose in order to conceal a murder, the Polish news agency PAP reported on Monday.

Investigators are almost 100 per cent certain that the explosion in the apartment building was on purpose and intended to cover the murder of a woman, PAP reported, citing a source in the authorities.

A state prosecutor would not officially confirm the information, though she did not deny that the explosion was intentionally caused.

The bodies of three women and two men were recovered from the ruins. In addition, 21 people were injured after three of the apartment building's four floors collapsed in the explosion on Sunday morning.

The wpolityce.pl online news portal reported that the body of a woman who had died a violent death was recovered from the building's ruins.