A 70-year-old man is in hospital in critical condition after his neighbour beat him up on Saturday night, say police.

Around 10:30 p.m. in an apartment building on Decarie Boulevard, a 27-year-old man beat the 70-year-old man with his fists, causing severe head injuries.

The younger man called 911.

Police were unsure if the assault took place in the hall of the building or in the victim's apartment, although they did confirm the two knew each other.

The 27-year-old is in police custody and is expected to appear in court on Monday to face charges of assault causing bodily harm.