Police have begun interviewing some passengers injured after a van ran off the Napier to Taupo Road, plunging 20 metres down a gully.
The van carrying eight people ran off the road near Te Haroto on State Highway 5 about 7am on Thursday.
It is believed a man fell asleep at the wheel after driving through the night to Auckland Airport to pick up five family members from Australia before returning to Hawke's Bay.
All in the van were injured and are being treated at Hawke's Bay Hospital.
The condition of a Melbourne baby has improved and he is now in a serious but stable condition on Friday.
A man in his 30s remains in a critical condition. A woman in her 30s and two girls, aged 8 and 9, are described as being in a serious but stable condition. Three other men are stable.
Senior Sergeant Stuart Fleming said police have not been able to interview the driver and the crash investigation into the crash will take several more days to establish what went wrong.
"We haven't been able to talk to the driver and we're getting information from family sources, so we need to confirm all that, have a look at the mechanical aspects of the vehicle before we can fully determine what we believe to be responsible for the crash."