Rescue crews believe the driver of a van that plunged down a gully had been driving through the night and probably fell asleep at the wheel. All eight have been injured.
Five passengers from Australia were travelling from Auckland to Hawke's Bay with three New Zealand family members when the crash happened just before 7am on Thursday.
A six-month-old boy from Melbourne is fighting for his life and a man in his 30s is also in a critical condition at Hawke's Bay hospital after the van came off the Napier-Taupo highway (SH5) near Te Haroto.
A man and a woman in their 30s and a nine-year-old girl are in a serious condition and have been moved to the high dependency unit. A 12-year-old girl is in intensive care in a serious condition.
Two other men, including one thrown from the vehicle with the baby, are in a stable condition in a general ward.
Hawke's Bay rescue pilot Jeremy Bruce helped winch the group to safety and said the rescue effort in the remote area was extremely difficult due to rough conditions.
Mr Bruce said the van veered off to the left, hit a bank and rolled into the 20-metre gully.
"It appears the male driver's been up to Auckland to pick up family members from Auckland Airport and were returning back to Hawke's Bay and that he's been driving through the night and fallen asleep at the wheel."
Mr Bruce said there were several cans of an energy drink lying around the accident site.
Senior Sergeant Stuart Fleming said the Napier to Taupo road is known for some danger spots and crews had huge difficulty rescuing the injured.
Hawke's Bay hospital spokesperson Anna Kirk said emergency staff were stretched to capacity when members of the group were flown in, as it is a busy time of the year.