The crowd packed Federation Square on Monday to reflect on the Bourke Street tragedy, a vigil held both in memory of victims and in support of those who survived.

"I see amongst your faces the diversity of our beloved city," Victoria's Governor Linda Dessau told the crowd, peppered with first responders, many who would have been on duty that day.

"Last Friday, tragedy did not distinguish on the basis of age, gender, culture, religion or background. But importantly, neither did goodness. On both sides of that ledger, we are all one."

Five people died - including two children - and dozens were injured when a speeding car raced along Bourke Street.

But the actions of bystanders, police and paramedics to help the many injured, and the thousands who have laid flowers near the scene since then has given many people hope.

Henry Dow, for instance, brought the crowd to the brink of tears when he read out his now-viral Facebook post at Monday's vigil.

He recalled surviving the CBD attack and being calmed by what he assumed was an emergency services worker.

But the man helping him and others was no paramedic. He was a cab driver.

"He took command and was a genuine hero," Mr Dow said.

"Many images and sounds will stay with me much longer than I might like, but I'm glad I've seen, and I hope I never forgot, just how brave strangers can be. I love this city."

The names of the victims were not spoken during the vigil.

But mourners laid an Australian flag on the stage. Then, one by one, people took turns laying flowers and teddy bears at the make-shift memorial.

Kelly O'Dwyer, representing Prime Minister Malcolm Turnbull, wiped away tears while Opposition Leader Bill Shorten and Premier Daniel Andrews were also visibly moved.

Catherine Jones, of Blackburn, said she first heard about the incident when her daughter phoned from her city office to say she was okay.

On Sunday, she visited the Bourke Street floral shrine to lay some pink roses and a card, in which she wrote, 'Sometimes there are no words'; "Because I just couldn't think of the words I wanted to say," she said.

Her friend, Felicity Kamenek, of Belgrave South, said it was the first time she had attended a public memorial.

"I am appalled, upset and angry that something like this happened in our beautiful Melbourne."

Siobhan Johns, of Montmorency, said she brought her son to the vigil to help explain the full picture of what had happened.

"I felt helpless. Having children, knowing a couple of kids died, I found that really sad," she said.

Ms Johns explained to her young son what had happened by showing him the skid marks in Flinders Street, the site of the tragedy and finally, the vigil.

"It was nice to be able to explain to him why people [gather like this]. It's not something he's ever seen before," she said.

Mary and Val Simpson were among the first to arrive, saying they wanted to stand in solidarity with fellow Melburnians.

"We need to show the world that we are one," Mr Simpson, 76, said. "We don't want anyone to think differently of us."

Mrs Simpson said her heart went out to those who died - and the emergency services workers who witnessed the dreadful aftermath.

"I couldn't believe this was Melbourne," she said.

"That's not my Melbourne. We've been coming to the city for over 70 years and always felt safe. Always. We were just stunned."

Rabbi Yehoshua Smukler, the principal of Beth Rivkah Ladies College, where 10-year-old victim Thalia Hakin was a student, said the vigil was a positive example of the Australian spirit.

"It was shocking just to hear it happened, it was shocking to hear a child had died and then when they heard a child was of our very own school it brought it to home," he said.

Rabbi Smukler said support from the school community had come from a broad range of religious organisations of all denominations, scout groups, other schools and psychologists.

"It's important to be able to talk about it with others and to grieve together," Rabbi Smukler said.

"We don't need to wait for tragedy to bring the community together but it really has been a tremendous display of unity and support."

He implored the community to move on but not to forget.

"We also need to realise that for us, our lives will move on and get back to normal but for the victims they will never be the same," he said.

"Don't forget about [the victims and their families] in a week or two when things settle down and life moves on because that's when they are really going to need our support."

Lord mayor Robert Doyle opened the vigil at 5.30pm.

Christine Kilpatrick, CEO of the Royal Children's Hospital, also spoke at the vigil, expressing regret that the hospital couldn't have done more.

"The great tragedy, of course, is that we couldn't save everyone injured in Friday's attack," she said.

"We have to live with this - and it's hard."

The vigil ended at 6pm with a minute's silence and the Josh Groban song You Raise Me Up.

The crowd stood in silence, wiping away their tears.

What they said

Maggie McDermott 61
"I just think it's nice to be all together. I felt I had to come down from Ballarat. I've got grandchildren of a similar age. I wanted to let them know I'm thinking of them and the families and everyone that's involved in this tragedy."

Stuart Roberts 61 
"The reason I've come down is because I'd like to pay my respects to that incredibly tragic loss of life on Friday and to show that as a member of the Melbourne community I care very deeply for the people that have been affected and hope that the folks in hospital have good and speedy recoveries. And just to know that they are loved and thought about."

Melissa Turnbull 
"Just because I want to pay my respects. I work in the Galleria building so I just wanted to say everyone's hurting and I feel sorry for the families and the people that were there and witnessed it all and the workers."

Maria Manago 46 
"Unfortunately the incident that happened on Bourke Street on Friday really touched home to how short our life can be and how we can lose it at the blink of an eye. Just innocent people going by their daily whatever they're doing and then to just lose your life just like that."

Cheryl Sadler 
"Tiarne and I were in yesterday to lay some flowers and it was just incredible, the mood was so sombre and we thought we just wanted to come and pay our respects to everyone that was caught up in the thing on Friday. It's just eerie, it hits really close to home that it could have happened to any of us."

Lynn Gordon 54
"I don't even know where to begin. I live work and breathe Melbourne. I'm passionate about Melbourne and its people and just torn apart that such a terrible thing could happen. It was really close to home." 

Mathew Rogers, Alicia Watson and Kylie Reed. 

Kylie Reed 28, Alycia Watson 28, Matthew Rogers 41.
Alycia: "We're here for the tragedy"
Kylie: "We saw it all on Facebook and just thought we'd come down and pay our respects." 
Matthew: "We've a four-year-old son as well so we thought we'd come down and pay our respects as there was a little kid involved." 
Kylie: "It's such a tragedy so it's always good to come down and pay your respects."

Josh Bull 31
"This is an opportunity I think for all Melburnians and all Victorians to come together in solidarity, in support of those that we've lost and certainly the families of those people that were tragically lost last Friday. I think it's an opportunity for people to pay their respects and stick together at what is a really difficult time for the state."

Donations to the immediate families of the victims can be made by calling 1800 226 226 or via the website: www.vic.gov.au/bourkestreet.html

For urgent support, call Lifeline on 13 11 14 for confidential 24/7 counselling and referrals.

Victoria Police is urging witnesses and victims requiring support to call the Victims' Support Helpline on 1800 819 817.