Surrounded by a heavy presence of police cruisers and security guards, hundreds of members of Montreal's Jewish community, politicians and other mourners gathered at a synagogue Monday to remember the 11 Jews murdered over the weekend in Pittsburgh.

The rabbi of the Beth Israel Beth Aaron synagogue, Reuben Joshua Poupko, watched as people streamed into the main prayer hall, filling every pew as well as the upstairs balcony.

"This is the most important statement," he said, acknowledging the size of the crowd. "There are members of all communities here. The Jewish community doesn't stand alone and it doesn't grieve alone. The pain is shared by many."

Multi-faith vigils commemorating the slaughter in the Pittsburgh synagogue were also taking place in Toronto and Edmonton.

Representatives from the federal, provincial and municipal governments were on hand for the ceremony in Montreal, which began at 7:30 p.m. with a song and a reading of the names of the 11 victims of the mass murder Saturday at Pittsburgh's Tree of Life Synagogue.

Police cruisers lined the streets around the building and the synagogue hired its own security guards to pat down every person in attendance.

Brenda Gewurz and her husband Samuel were on the balcony overlooking the main prayer hall.

"Montreal is a very close-knit Jewish community," Brenda Gewurz said, "And we stand in support of our communities across the world."

"It's a very sad day and I think it's important that we acknowledge the sadness."

Earlier on Monday, leaders of a mosque in Quebec City that was the site of a 2017 mass murder carried out by a lone gunman sent condolences to Pittsburgh's synagogue.

"It reminds us of the difficult moments we went through, and it brings back some of that worry," Islamic Cultural Centre of Quebec co-founder Boufeldja Benabdallah said in an interview Monday.

In a statement, the centre's board decried "the madness of men" that "struck our Jewish neighbours of Pittsburgh ... who were only praying in a sacred and untouchable place .... Today we understand very well the pain that Jewish families feel, and we are wholeheartedly with them."

In Ottawa, Prime Minister Justin Trudeau said Canadians are "horrified" by the Pittsburgh attack, which occurred at a Sabbath service.

"Our hearts are with the Jewish community in Pittsburgh and across Canada," he told the House of Commons. "May the families of those murdered be comforted and may the injured recover quickly and fully. We're working with U.S. authorities and ready to assist if required. Mr. Speaker, we will always stand united against hatred, intolerance, anti-Semitism and violence."

The January 2017 attack at the Quebec City mosque killed six worshippers and injured 19 others.

In the months since the attack, Benabdallah said, a new reality has set in at the mosque. Open doors have given way to concrete barriers near the front door, magnetized locks and security cameras.

"What more can we do? It's terrible," Benabdallah said. "Are we going to keep on living like this, barricaded?"

But he acknowledged such measures are necessary "until such time as things calm down and return to normal."

Monday's vigils follow similar gatherings Sunday in Halifax, Vancouver and Ottawa. More events are planned Tuesday in Winnipeg and Hamilton, Ont.

In Ottawa, more than 300 people packed into the Soloway Jewish Community Centre for a memorial service, lining the walls and taking every available chair -- except 11, left vacant on the stage, each bearing the name of one of the victims.

Dena Libman, whose cousin Joyce Fienberg was among those killed, addressed the crowd of residents, religious leaders and politicians from all parties and levels of government.

She said that in the Jewish world, it feels like everyone is a member of the same family -- it's just that some are closer than others. Fienberg grew up in Toronto.

More than 100 people attended a vigil at Shaar Shalom Synagogue in Halifax Sunday.