"I thought to myself, over and over, 'I'm alive. I'm okay'."

That was how earthquake survivor Ann Bodkin, 54, kept up hope during her 26 hours entombed in the mangled mess of the collapsed Pyne Gould Corporation building in central Christchurch.

She was at her desk in a corner of the third floor when Tuesday's earthquake shook the building ferociously.

"I realised straight away that it was going to be a big one," Ms Bodkin told the Weekend Herald. "I thought, 'This is it'."

She went to dive under her desk, but as she did, the ceiling collapsed and she was struck in the back of the head and on the shoulder.

"I was hit again in the back as I got under my desk and it knocked me to the floor."

The desk was crunched under the weight of the collapsing ceiling, but held up just enough to save Ms Bodkin from serious injury.

"If I had been crouching under the desk I might not have survived.

"It seemed to happen very fast, a huge noise, briefly, and then total silence.

"I started calling out to see if anyone else was around, but there was only silence."

Ms Bodkin tried to reach her cellphone, but it had been on her desk and was under the rubble.

Trapped in a space about 2m long under her L-shaped desk, she forced herself to stay determined to survive.

"I could move my arms and legs, and I had a little room, and fresh air. That's when I thought, 'I'm going to get out of here alive', and I remained that way the whole time I was trapped. I had to.

"I thought to myself, over and over, 'I'm alive. I'm okay'."

Ms Bodkin started calling out, but realised she might need her voice later, so she started banging a large piece of Perspex against a nearby radiator. There was no answer. Hours passed.

"The worst thing was that the sprinklers came on three times when the rescuers were drilling.

"I was worried I would fall asleep and get too cold, so I tried to stay warm by doing exercises, rubbing my arms, moving my legs.

"I was shivering and cold. I was wet the whole time."

She thought of her husband, Graham Richardson, and clung to the memories of their four-month holiday last year to America and Europe.

"And I was thinking about all the holidays we would have in thefuture."

Night fell. About 10 people were pulled to safety in the first night, but Ms Bodkin was not found.

It was a change of rescue team the following day that gave her a chance to communicate with the outside world.

Just before midday, after almost 24 hours since the building collapsed, there was a lull in the noise outside. She cried out for help.

"They had turned the machines off. I called and I heard someone say, 'Is that someone calling from in there?' I called again.

"I was hugely relieved. That was the first time I cried."

Rescuers contacted Mr Richardson and he arrived soon afterwards.

It took some time to find her exact position, because the tangled debris made it difficult to establish where her voice was coming from.

Rescuers thought she was 10m from the edge of the building, but it turned out she was 20m in.

They used a stick to pass a water bottle to her, then cut a hole in the wall to free her.

She then had to inch - on her back, feet first - through the debris to the light.

Just as she was about to reach her freedom, a nasty aftershock gripped the building once more.

"We thought, 'Oh no, not now," Mr Richardson said.

"It had been a two and three-quarter hour rescue. To lose her at that stage would have been horrific.

"But the rescuers didn't budge. They looked at her and said, 'We're going to get you out'."

The aftershock subsided and she emerged just as the sun came out.

She was wrapped in a blanket, attached to the end of the fire truck ladder and lowered to the ground to medics, rescuers, and a beaming Mr Richardson.

"I remember lots of faces staring, and then getting a glimpse of my husband. That was fantastic. He said something to me, but I had a neck brace on and all I could do was giggle. I was just so happy."

Said Mr Richardson: "I told her I'd thought I'd lost her forever. And I told her I loved her. It was very emotional. Just unreal."

They thanked "everyone who was involved in the rescue".

Ms Bodkin is recovering from cracked ribs and bruises.

Mr Richardson said he was coming to terms with people being in awe of his wife for surviving her ordeal. "She doesn't think so, though. She just thinks she did everything she could do to stay alive."