Northland police spokeswoman Sarah Kennett said the 67-year-old man's injuries were not life threatening so he was taken by road to Whangarei Hospital.
However, his condition deteriorated and he died early yesterday morning, about 12 hours after the crash. The driver, aged 69, was uninjured.
Experts from the police Serious Crash Unit carried out a scene examination yesterday.
Police were contacting relatives overseas before releasing the man's name. They would also wait until the investigation was complete before commenting on the possible cause, Mrs Kennett said.
It is believed the couple had been staying at Waipapakauri with family members before heading south.
The man's death brings the provisional Northland toll for the year to date to three. He will be removed from the road death statistics if a post-mortem examination later finds he died of medical causes.
The other fatalities were a 50-year-old Whangarei motorcyclist who crashed near Tangowahine on January 5 and a nine-year-old Auckland boy whose go-kart rolled on Ninety Mile Beach on January 10. Beaches are legal roads so beach crashes count towards the road toll.