The 'harrowing' crash happened in Hawke's Bay about 1pm on Saturday.
Police said a police patrol on the outskirts of Waipawa recorded a vehicle speeding into the city at 80mph.
The patrol turned to follow the vehicle and shortly afterwards saw that it had crashed head-on into another vehicle on High Street (State Highway 2).
Three people were taken to Wellington Hospital, two of whom were in a critical condition.
Police said they were in critical condition on Sunday afternoon.
The third person taken to Wellington Hospital suffered minor injuries and has since been discharged.
A fourth person was taken to Hawke's Bay Hospital where he remained in serious condition on Sunday.
According to police, a dog was in the car and suffered minor injuries.
It was taken to a local vet for a check-up and has since been handed over to its owners.
According to the police, the accident was probably caused by excessive speed.
A 19-year-old man was arrested at the scene and charges are being considered.
“Incidents like this are distressing for everyone involved, including the victims, their families, members of the public who witnessed the crash and first responders,” said Lincoln Sycamore, Hawke's Bay Area commander.
“We are providing support to those affected and our investigation into the circumstances of the crash is ongoing.”