Montreal police arrested three people for assaulting officers, one for wearing a mask and about 30 as "preventive arrests" at a midday anti-austerity protest on Rene-Levesque Boulevard downtown near the Queen Elizabeth Hotel.

Police say protesters tried to enter an office building. A scuffle broke out after officers arrested a demonstrator for wearing a mask, violating the municipal P-6 bylaw. One officer suffered minor injuries to his jaw.

Police then surrounded all the demonstrators, containing them on Réne-Lévesque Boulevard. The street was closed for a time between Peel Street and Robert-Bourassa Street.

Police searched demonstrators and loaded them onto a city bus.

Police spokesperson Ian Lafrenière said the demonstration was declared illegal and most of the arrests are preventive. Lafrenière says the majority of demonstrators will be released without charge later.