A woman found slumped in the driver's seat after a crash which left eight people needing hospital treatment had a cellphone in her hand.

A baby and a pregnant woman were among those taken to hospital after the accident on White Swan Rd in Lynfield, Auckland, around 11am yesterday.

Police are investigating how the woman came to be found with the cellphone in her hand.

They are looking at whether she was using it just before the accident or if she had grabbed it to call emergency services before becoming unconscious.

Sergeant Steve Chung of Balmoral police said a witness who ran to the scene to help found the Audi driver unconscious behind the driver's wheel.

"The driver ... has no recollection whatsoever of what happened. Last thing she remembers is taking the kids to get some school uniforms or something like that," he said.

"That could be from a bang to the head, or just shock, but we need to follow some lines of inquiry regarding the witness who stopped."

Mr Chung said it was possible the woman had crashed and grabbed her phone to call for help before falling unconscious. Or it was possible she had been holding the phone down on her lap using it, which could have caused her to veer to the right.

But these possibilities were purely speculative and it would take time to talk to witnesses to find out what happened, he said.

The 42-year-old woman was driving along White Swan Rd when her car crossed the centre line and collided head-on with a Suzuki Vitara, just before the intersection of Hillsborough Rd.

Traffic was diverted around the scene for almost two hours while emergency services cleared debris.

The smashed wrecks were left, bonnets touching, having narrowly missed hitting two parked cars.

Mr Chung said the woman's condition was initially listed as critical but she improved yesterday.

Six children aged between 21 months and 12 years were taken to Auckland City Hospital for checks but escaped with minor injuries.

The pregnant woman, 32, was also cleared by doctors last night.

Waitemata road policing manager Superintendent John Kelly last night stressed the need for drivers to not be complacent about texting or speaking on a cellphone while driving.

"They're just getting blase about it, so we need to reinforce that message.

"Research and evidence shows that if you're using a cellphone while driving, you're far more likely to crash than if you're not."

Mr Kelly said many people had a tendency to want to answer the phone straight away, a reflex almost, that could potentially lead to an accident.

"Either pull over and answer it or just let it ring.

"Is the world going to end if you don't answer it?"

- additional reporting: Vaimoana Tapaleao