A spokeswoman for Christchurch Women's hospital said 21 babies were born at its maternity ward in the 24 hours after the tremor, which damaged buildings and roads in New Zealand's worst quake disaster in decades.

"In the 24 hours post earthquake, 21 babies were born at Christchurch Women's hospital and that's a record for a Saturday," a hospital spokeswoman told AFP, without offering an explanation.

The first newborn arrived within 10 minutes of the quake, which saw roads gridlocked as residents rushed to higher ground to escape a potential tsunami.

Meanwhile Miriam Garcia was in labour at home when the quake struck and had just decided to head for the hospital.

"I couldn't believe the timing," the new mum, who delivered baby Amelia about two hours later, told The Press newspaper. "I had a lot of false labours in the weeks before and I was thinking, 'Now it's happening?'"

Danika Weeks was already in labour in the hospital when the earth rocked.

"The first thing I remember was seeing the re-sus (resuscitation) machines sort of coming towards us, like two horses racing towards us," she told TVNZ.

"I was sort of like, 'Gosh did we cause this? You know, is this part of it? Does the earth move?'"

Baby boy Lincoln arrived safely, and first-time mum Weeks said she suspected the shock of the quake was enough to jolt others into delivering their newborns.

"If you weren't in labour already it definitely would've brought it on for sure," she said.

Of the experience, she said the quake "made it all the more amazing, really, that we went through two sorts of trauma in the one day".