Three-year-old Jett Mitchell hadn't slept in his own bed since the September earthquake and was receiving counselling on the fifth floor of the Canterbury Television building when the quake struck Christchurch.

Yesterday, his mother, Kendyll Mitchell, said it was a miracle that Jett, his 11-month-old sister, Dita, and she survived a five-floor plunge in a building that was reduced to rubble.

The three arrived early for the counselling session, shortly before the quake measuring 6.3 on the Richter scale devastated the heart of Christchurch.

Ms Mitchell said her son had suffered "severe anxiety" since the first quake in September and she was in the building to get him help.

"We had had six months of hard times. He wouldn't sleep in his own bedroom."

As the CTV building collapsed, Ms Mitchell sheltered Jett with her own body. Dita was protected by her stroller.

"I got knocked out at the bottom. I thought we were all gone. When I woke up, they were both staring at me. They were covered in my blood.

"I instantly smelt smoke. All I thought was the building was going to fall on us, the steel was going to fall on us."

Ms Mitchell had a cracked pelvis and a deep leg gash, and was partially trapped in the rubble.

But Jett had only scratches on his chin and knee and Dita was unscathed.

More than 100 others in the CTV building were killed or are missing.

Ms Mitchell was carried from the rubble by a builder who had been working at the site.

"I couldn't get the rubble off. All I could see was sky. I remember saying to him, 'How is it?' and he said, 'You are OK, you are OK'."

Her children were carried from the scene by passers-by. "They're both unhurt. It's a miracle," she said.

Ms Mitchell was photographed by the Christchurch Star as she was carried from the scene by her partner's friend, Mark Hoskin.

She said the photograph showed what it was like on Tuesday last week as crowds of people fled the city centre.

Ms Mitchell got out of hospital yesterday, and the family are now recuperating in Timaru, where she has family. "I am pretty emotionally broken," she said.

But her children are doing well. She said Jett was "back to normal" in quake-free Timaru and was sleeping in his own bed.

"He's been awesome. We're very lucky. My little family is still my little family.

"We are going to relocate [to Timaru]. No hesitation. I can't go back ... for his mental benefit, and mine."

Ms Mitchell said she was grateful for the help of the builder who found her in the rubble, and wanted to contact him to say thank you.

She has also thanked Mr Hoskin, who is playing down his part in the rescue.

"There are people out there who have done massive contributions. I was just around," he said.

Mr Hoskin was on the roof of the Les Mills gym, next to the CTV building, looking at air-conditioning units when the quake struck.

"We didn't see the [CTV] building come down but we heard it ... It was pretty terrifying."

He described the noise as a "really loud roar".

Mr Hoskin got down to the street and heard Ms Mitchell calling him.

"I'm friends with her partner. It was so completely random."

He said people were working furiously to pull survivors from the rubble.

One of those rescued was Ms Mitchell.

"She couldn't walk properly - she tried hobbling but it wasn't working," Mr Hoskin said.

"They were in a state of shock more than anything."

He scooped Ms Mitchell into his arms and carried her towards a triage station in Latimer Square where doctors were providing first aid.

Mr Hoskin waited for a while, but had to leave to pick up his own son from preschool.

Search and rescue workers were still at the CTV building yesterday, searching for bodies.

Nine days after the quake, dozens of people thought to have been inside the building remain missing.