A memorial service to commemorate the 75th anniversary of the Ballantynes department store fire will be held at the Christchurch Transitional Cathedral this evening.
It was mid-afternoon on the Tuesday of Carnival Week in what was then New Zealand's third largest city.
Hundreds of staff and shoppers packed into the Ballantynes department store and its tearooms when a fire broke out in the basement.
A crew from the National Film Unit was in the city for the Carnival Week races and captured the horrifying scenes of what followed.
Historian Tony Phillips said the fire could have been burning for half an hour before the fire brigade was notified.
A succession of errors meant many staff were still working as the fire crept through the wooden structures of the massive complex filled with highly flammable materials.
"They thought they were dealing with a small fire in the basement," he said.
"Unknowingly, the fire was spreading through the basement up stairwells and up lift shafts into the rest of the building and filling it with smoke. When it did blow and people did try to get down stairs, they couldn't."
A flashover occurred about 4pm, causing the building to erupt into flames with explosive force, Phillips said.
As a result 40 people were killed by the raging inferno.
Another, Violet Cody, was fatally injured when she leapt from the burning building.
She later died in hospital along with her unborn child.
"When you see the mass grave and the memorial down at Ruru Lawn Cemetery, it brings the enormity of it into focus," Phillips said.
Working on the top floor was Marion Hooykaas. Now 92, she had joined Ballantynes as an apprentice tailor at just 17.
Fire engines and people were already gathering on the streets when she was given the order to evacuate, she told RNZ.
"There was a small stairway right next to the cafeteria and I said 'We'll go down there, it'll be quicker' . . . and Bill, the young guy making the caps, he had his hand on it and he said 'You can't go down there. Those stairs are on fire'."
They found another way out as the fire took hold of the building and Hooykaas, along with the rest of the team she worked with, managed to escape.
"It was slow going down the stairs. I can remember saying 'I hate going out in the dark' because it was so dark and smoky going down those stairs to Cashel Street," she said.
She emerged to find a mass of people looking on in horror.
"Everyone just couldn't believe it," she said.
"We just couldn't believe it when we saw all these people when we got down and I counted 11 fire engines along Cashel Street."
She realised how lucky she and others working alongside her were.
"Probably all of the others were dead on the other side [of the top floor] when we got down."
The enormity of the tragedy became clear to her the next morning.
"We used to have a dairy treatment station and the milkman used to come with all their crates of milk, and I woke up and heard him saying 'There's a lot dead, there's a lot dead, it's bad'. That's what I woke up to," Hooykaas said.
"It was sad. That was the first big funeral I had ever been to, of course."
In the days following the city was gripped by grief.
The streets of Christchurch were lined with mourners as the funeral procession made its way through the city.
An estimated 10,000 people attended the funeral at Ruru Lawn Cemetery.
Ballantynes chief executive Maria O'Halloran will this morning lay a wreath there - as the company did every year.
The dark period in the company's history still affected staff today, she said.
"Sometimes it's a really emotional response from the staff, especially if there is a family or friend connection. Others are respectful and very supportive because we recognise this is a part of our history, and we do so every year. This event, as I've said to many, will always be etched in our DNA."
The memorial service at the Christchurch Transitional Cathedral begins at 5.30pm.