Hundreds of Calgarians came to Olympic Plaza Sunday night to mourn and show support for the victims, survivors and families of the largest gun massacre by a single shooter in U.S. history.

It's also about standing in solidarity with the LGBTQ community.

Omar Mateen, 29, shot and killed 50 patrons of the Pulse nightclub early Sunday. Dozens more are injured.

One of the Calgary organizers says she was shocked when she woke up this morning and checked social media.

Organizer Visa Dekline said it's important to send a message of support and solidarity. (Kate Adach/CBC)

"I woke up in the morning and … I saw friends of mine in other cities and Orlando … that were marked safe on Facebook using the safety check feature and I was wondering what that was all about, what happened," Visa Dekline tells CBC News.

"Then I read in the news the horrible situation that happened at Pulse nightclub last night. The fact that it happened during Pride month around the world and that it was targeted to a gay bar," she said.

Organizers put the vigil together in just a few hours. (Kate Adach/CBC)

Dekline said it's important to send a message.

"I think it is really important for the community to come together to mourn, to heal, to be with one another and to show the rest of the world that it's not going to phase us. We are stronger. We are louder. We are not going to be oppressed by one act of gun violence."

'Hits all of us at our core'

Jackie Dowdell learned of the attack at about 6 a.m. on her way to work.

"It hits all of us at our core," she said.

Jackie Dowdell said the shooter's hatred spilled over into violence where 50 people were massacred. (Kate Adach/CBC)

"I think I was saddened by the fact that, here we go again, yet another community was targeted. It seems that, we are not just the community itself that is targeted, but again the human race is targeted by gun violence, by hatred."

Mateen's father told media his son had witnessed two men kissing, which may have set him off.

"For this individual his hatred spilled over into violence that affected the lives of more than 120 people and many, many more with 50 individuals massacred that night. The tipping point in this seemed to be, two individuals engaging in a romantic situation, a kiss, that set someone off that had beliefs that are different from most of the world," Dowdell said.

Speakers talked of the need to come together. (Kate Adach/CBC)

"People have the right to love who they love."

Calgary landmarks like the Calgary Tower and Langevin Bridge were lit in rainbow colours to mark the tragedy.

About 500 people attended the Calgary vigil, joining others in cities like Edmonton, Vancouver, Toronto and Ottawa.