09/12/2011 01:18 EDT | Updated 11/12/2011 05:12 EST

Police arrest man in Westmount bank robbery

A bank robbery in Westmount, Que. forced police to set up a wide security perimetre Monday including Sherbrooke Street West.

Police said at least three or four suspects armed with a stun gun robbed the Toronto Dominion Bank on the corner of Greene Ave. and De Maisonneuve Blvd.

One woman was treated for shock after the robbery, and police are trying to determine whether she was hit in the face with the stun gun.

The suspects fled the scene, but were followed by a witness on a bicycle.

The bank robbers hit the witness in the face and took his wallet before jumping into a car to leave the scene.

A few kilometres west of the robbery, at the corner of Sherbrooke St. and Melrose Ave. in Montreal's Notre-Dame-de-Grâce neighbourhood, the car smashed into a van.

Montreal police were able to arrest one of the suspects, a man in his 20s, but are still searching for at least two or three others.