A mother of three who almost killed her children and two young relatives when her car drifted off the road has spoken out to warn other motorists about the dangers of driving when tired.

Antoinette Ranapia, 34, of Auckland was on her way to visit her parents in Whakatane when she believes she fell asleep at the wheel.

She had had a late night and was about three-quarters of the way to her destination last Saturday afternoon when the accident happened.

Ms Ranapia was knocked unconscious and woke up lying on grass with her children scattered and crying.

"My children were to the left of me. I was on a grass verge. A helicopter was coming in to land on my right. There were a lot of people around. A lot of paramedics. It was full-on.

"I was crying, my children were crying," Ms Ranapia said. "It was so quick. I couldn't believe it."

At first, she failed to grasp what was happening.

"A few minutes later, I was still thinking, 'I'm on the grass. Here I am looking at my children, lying on the ground, crying. The paramedics are talking to them'.

"Then I thought, 'They're responding. They're all responding'."

Her 11-year-old cousin, who was on the car, was flown to the Starship hospital in Auckland and has undergone two operations.

Also hurt were Ms Ranapia's sons aged 11 months and 4, her daughter, 8, and a nephew, aged 7.

The whole family were in Tauranga Hospital for about 24 hours receiving treatment.

Ms Ranapia said the only breaks she had made during the drive from Auckland were to breastfeed her baby.

At the crash scene, 20km east of Te Puke on State Highway 2, a rugby team from Te Puna helped the family while a truck driver blocked the road to protect them from traffic.

Police, firefighters, paramedics and members of the public assisted, including providing blankets for the children.

"I just want to thank all the people who helped my children and me after the accident, who were all absolutely amazing and I'm so thankful," Ms Ranapia said.

Everyone in the car had been wearing seatbelts, she said.

She would not be driving with any passengers for a while - and certainly not when tired.

"I definitely should have pulled over. It was not the trip I wanted. Don't drive when you're tired. I can't stress that enough."

Ms Ranapia said her children were a little rattled, but eager to get back to school.

"My children tell me, 'Mum, you crashed', and I just say, 'Yes, I did. I'm very sorry'."

Her partner drove the family back to Auckland yesterday.