As windows smashed and the building shook and dropped beneath her, Kristy Clemence ducked under her desk and thought of how she would get to her 1-year-old daughter, Zara.

Last night, still stunned and shaken from her ordeal, the woman at the centre of a miraculous earthquake rescue was still thinking of her daughter as she took her home to bed.

The 32-year-old executive assistant was plucked by firefighters from the rooftop of the Pyne Gould Corporation building, which collapsed on Cambridge Terrace.

More than 30 people are believed to be trapped in the building - three of them Ms Clemence's workmates at insurance broker and risk advice company Marsh.

Ms Clemence arrived at her parents' home without her shoes, wearing torn black stockings and with white dust all over her "like on September 11".

She described a horrifying experience, as she lay on a steep angle, under her desk on the collapsed building's floor.

"I was just working and then just felt what I thought was an aftershock and then it just got worse. I looked around and I could see the glass smashing so I just dived under my desk ... It felt like we dropped.

"It went 'boom boom boom' like you were dropping and then everything just slid ... the whole building collapsed.

"My desk saved me, I think. It was just probably the best thing to do. It's what you learn at school, isn't it? You just dive under your desk. So it's obviously saved my life. I jumped under my desk ... I was just thinking I need to get out to my daughter. I just need to be strong for her.

"My phone was about two metres down from me on the floor and I could see it ringing and I didn't know if I should climb down to get it. I thought if I could just get down to the phone, I could just call someone. But I couldn't.

"I'm just very, very lucky. I could just see through the roof to the sky. I couldn't see the Pricewaterhouse building so I thought all the other buildings around us must be flat.

"It felt like we could be there for days. I didn't know if I kept moving, things might start getting worse. I thought I would cause more things to collapse and they could fall on other people. I didn't know what to do.

"I was able to climb through a hole on the roof. I could see the sky so I just climbed out through that [hole]."

Ms Clemence was then able to yell out to rescuers. She said she had not seen dramatic television footage which shows people telling her to stay still on the flimsy building as firefighters extend a ladder to bring her down.

"I'm fine, I'm just still in shock," she said last night.

"I'm just worried about my colleagues; they're still in the building.

"I've got a little 1-year-old daughter so I was just worried about her more than anything. She's at that age where she doesn't know what's going on, so it's lucky."

Ms Clemence's mother, Valerie Clemence, described an anxious three-hour wait before she knew her daughter was alive.

She "almost collapsed" when she heard on radio that the Pyne Gould building had collapsed, knowing her daughter was inside.

Fearing another earthquake, she didn't want to go inside her home, so she began pacing.

"There's liquefaction on our lawn and all you can see is footprints where I've gone up and down."

Kristy Clemence's partner, Julian Johnston, also had an anxious wait - first to hear if Zara was safe in her central city childcare centre, then for news of Ms Clemence.

Because cars were blocked from the city, he first rode a bike to find his daughter, then came back to get a car to start his hunt for her mother.

Hours later, she called him from a colleague's phone. They met up and he took her home.