A Catholic priest was stabbed during mass in front of his congregation at Canada's largest church.
Father Claude Grou, 77, received minor injured in the altercation during a morning service at Montreal's St Joseph's Oratory.
Video of the attack, which was being broadcast live, shows a man in a baseball cap rushing the priest as he stands behind the altar.
The man was quickly detained by the church's security team.
Authorities arrested a 26-year-old suspect who they say is known to police and will be questioned on Friday afternoon.
There is no clear motive for the assault.
Video of the attack, which took place around 8:30 am local time (12:30 GMT) on Friday morning, shows the suspect walking up quickly up to the priest, who is standing behind the altar performing the daily mass in the Oratory's Crypt Church.
The priest runs to the left, is chased by the suspect, and falls as the pair briefly tussle.
The suspect then moves away from him and is approached by a number of men who usher him away as the Father Grou stands up.
About 60 people were attending the service when the attack took place.
Father Grou was brought to hospital with what Montreal police described as "lacerations" on his upper body. His life is not in danger.
A number of politicians extended their prayers to Father Grou wishing for a quick recovery, including Prime Minister Justin Trudeau.
What a horrible attack at Saint Joseph’s Oratory in Montreal this morning. Father Claude Grou, Canadians are thinking of you and wishing you a swift recovery.— Justin Trudeau (@JustinTrudeau) March 22, 2019
Montreal Mayor Valerie Plante called the attack "horrible and inexcusable".
A small Catholic digital television station broadcasts the daily mass from St Joseph's Oratory each morning and clips of the attack were later obtained by Canadian news networks.
The historic shrine is a famous Montreal landmark and the largest shrine dedicated to Saint Joseph in the world.
It was founded by Brother Andre Bessette who was canonised by Pope Benedict in 2010 for his devotion to the sick and disabled.
About two million people visit the church each year.