The crippled frame of Pyne Gould Corporation House stoops over the banks of Christchurch's Avon river.

Eleven days on from the bedlam of February 22, rescue workers continued to claw tirelessly through the mangled wreck of concrete, steel and glass.

When the roof fell in on that violent Tuesday afternoon, more than 100 workers were inside. Up to 18 are still trapped in its clutches.

During last September's 7.1 magnitude earthquake, the 1960s building escaped unscathed.

This time, it "pancaked" in the tremors - the stairwell that ran up its centre now leans precariously over the rubble below.

The building housed a mix of insurance brokers, accountants, lawyers and public sector workers.

It was a close-knit environment - three of the firms within were owned by the same parent company and all had been in the same building for over a decade.

A former chairman of Pyne Gould, Sam Maling, moved his private law firm into the PGC House after leaving the company.

Many who worked there knew someone from another part of the building - conversations were had on the stairs and lifts as staff came and left the building.

It was one of these times when the quake struck - many had just stepped in from lunch at the central city's popular cafes.

Some, luckily, had not yet come back to work.

The 1pm lunch plans of the accountants at Leech & Partners meant co-director Glen White was only moments away from leaving the building when his second-floor office began to shake.

"It started and it just got worse. As I got under my desk the roof came down and when the dust settled, the floor above was just 10cm above my desk. Around me were roofing tiles, air conditioning units, files - all I had was a cavity under my desk," Mr White said.

The deafening noise of the sky falling in was replaced with terrible silence, only broken by the intermittent beeping of Mr White's cellphone, out of reach on the desktop above.

Unlike so many of those trapped in complete darkness, a shard of light illuminated the devastation of Mr White's office. But he could see nothing of the six who had been sitting in the open place workspace outside his door.

He called out to a colleague in an adjacent office and relief struck him when he heard an answer.

They prepared each other for the worst - they knew the danger of aftershocks was very real.

"I said to Chris next door, 'We could be here a while, we don't know if there's a hundred buildings down in the city.' With our one going down, we thought there would be more and it could take [a lot more] time for them to get us out," he said.

The pair had no idea it would only be an hour before they heard the calls of volunteer firefighters, only metres from them, up the side of the building.

When Mr White made it out to the ground, he was joined by those who had managed to clamber out of the wreckage - including three of his colleagues at Leech.

Marsh employee Kristy Clemence squeezed through concrete and debris onto the Pyne House's sunken roof, clinging for dear life until she was carried to safety by the Fire Service.

Helen Guiney, an accounts admin for Perpetual on the floor below, was not so fortunate - it would be nearly 21 hours before she would be carried out from the pitch black space under her desk.

Ten others who worked on her floor have still not been found.

Ms Guiney had returned from lunch early, her handbag not yet off her shoulder when the floor began to move - she still had it with her when she emerged from the building after her night trapped in the rubble.

"[Over 21 hours] strange things go through your mind - I don't know if I slept or if I passed out, but time seemed to go very quickly. My stupid cellphone keep ringing but I couldn't reach the thing. I knew it was six o'clock the next morning when my [cellphone] alarm went off," she said.

Her night was punctuated by aftershocks.

"The aftershocks were horrific and you think 'I'm fine now, but the next one could flatten everything'. You feel completely numb," she said.

As Ms Guiney was grabbed from the mangled remains of Pyne Gould, the last employee to escape from the building alive still lay cold and shivering on the third floor.

Ann Bodkin spent 26 hours buried in the rubble alone - rescuers had got to five other staff at the Education Review Office within hours of quake, but failed to locate her in the tangled mess.

The building's sprinklers went off three times, drenching her clothes. She was afraid to sleep. But despite not knowing if anyone was coming for her, Ms Bodkin refused to give up hope.

" I remained that way the whole time I was trapped. I thought 'I'm going to get out of here alive,"' she said.