Less than an hour after a 3-year-old insisted her nana drive her home, the pair were fighting for their lives following a car crash.

Firefighters had to cut grandmother Melissa Sinclair from her wrecked car after the accident a week and a half ago, Stuff reported.

The single-vehicle crash on in Sanson, north-west of Palmerston North, left Sinclair with a cracked skull, broken ankles, legs and ribs.

Every bone in her face is broken, with the smash breaking both of her shoulder blades.

She remains in a critical condition in Palmerston North Hospital.

Her granddaughter Avery has a broken back, damaged neck ligament, bruised bowel and a bruised spinal cord from the accident.

The 3-year old, in Starship Hospital, may never walk again, mum Rochelle told Stuff.

"Whenever we touch her toes or tickle them she doesn't react," she said.

Her grandmother suffered brain damage and it's too soon to tell if it was permanent. The physical injuries were expected to heal.

The Serious Crash Unit is investigating the crash, police told Stuff.

"The wearing or not wearing of proper restraints is part of the ongoing investigation into the incident."

Avery's mother Rochelle - who didn't want her last name used - told Stuff the family were leaving Palmerston North's Cloud 9 Trampoline Park when Avery insisted her nana drive her home.

But just before 4.30pm on Sunday February 16, she saw the wrecked car on the side of the road and drove straight to hospital.

"We saw the car on the other side of the road with the roof and the doors cut off," Rochelle said."

Her daughter was flown to Starship the next day, where she has slowly recovered and even awoke to speak top her parents.

A Givealittle page to help ease costs for the child and her grandmother has been created by family members.