"She said she took the baby off him and he just collapsed," an officer at the scene said.
Both were taken to hospital in a critical condition.
Down the bank, other injured people escaped the van.
"With the vehicle rolling and ejecting people and luggage, and belongings, it would be pretty chaotic," said station officer Peter Draper of the Napier fire brigade.
Six other survivors were winched to safety, and one firefighter who helped rescue them was amazed that no one had died.
Three rescue helicopters were sent to help.
The Lowe Corporation chopper winched four passengers from the scene, and took a woman and girl with spinal injuries to hospital.
A helicopter spokeswoman said the driver of the van had fallen asleep. Pilot Jeremy Bruce said several cans of energy drink were found lying around the accident site.
Five of the injured had arrived from Melbourne and had been picked up in Auckland by family members who were taking them home when the crash occurred about 6.45am yesterday on State Highway 5 about 80km from Napier.
Senior firefighter Shane Cunningham was winched down the bank with a colleague. Although he knew how many patients needed help, it was still startling to see the injured around the wreckage.
Mr Cunningham said they were all able to talk.
"The father was asking about the condition of the others. We spoke to them to comfort them and keep them alert."
He said it would have been impossible for the man found on the roadside to have climbed up with a baby, as previously reported - "it was almost vertical".
The crash could have gone unnoticed for hours if the two hadn't been thrown free. The van appeared to have gone out of control rounding a bend and hit a kerb, before veering across the road, overturning and bouncing over the cliff.
Skid marks and some glass and debris left evidence on the road, but the wreckage was in bushes and trees at the bottom of the drop and could not be seen from the highway.
All eight were admitted to Hawke's Bay Hospital.
The man, in his 30s, remained in a critical condition today.
The baby's condition had improved overnight to serious but stable.
A 9-year-old girl had also improved and was in a serious but stable condition. A man in his 40s remained stable, a woman in her 30s had also improved and was now in a serious but stable condition, as was a man in his 30s.
A man in his 20s remained in a stable condition and an 8-year-old girl was in a serious but stable condition.
Meanwhile, police say "the same old mistakes" are being made as the holiday road toll increased to seven with the death of a motorcyclist near Taihape yesterday.
"The basic messages about slowing down, not driving when you're tired, no alcohol, making sure all the vehicle occupants are safely restrained - all these things apply," said Assistant Commissioner Dave Cliff.
