A person is in a critical condition after a crash in Hunua, south of Auckland, and another person has been seriously injured in a crash near Palmerston North.
Police are warning this year's holiday road death toll is already the worst in four years.
Emergency services were called after a car went off the road on Middleton Rd in Hunua about 4.40pm.
One person was taken to Middlemore Hospital in a critical condition while two others had minor injuries.
Police said the road was blocked and diversions were put in place.
Separately, earlier this afternoon, a person was taken to hospital by helicopter with serious injuries after a four-car crash near Ohakea Airbase.
It happened on State Highway 1 between Sanson and Bulls, blocking the road completely.
The road has since been cleared but motorists were warned there might still be delays.
Worst holiday road toll in four years
Nineteen people have died so far during the holiday period, which ends at 8am on 4 January.
The number of deaths in the same period four years ago (2012/13) was six, the lowest ever.
Assistant Police Commissioner Dave Cliff said this afternoon the toll had been rising ever since.
People were ignoring simple road safety messages, and that had resulted in some of the deaths these holidays, he said.
"The basic need to wear a safety belt, the need to slow down, not to drive after you're drinking alcohol... The things all of us seem to take for granted.
"A small group don't, and unfortunately they don't just kill themselves, they kill their passengers, they kill other innocent road users including pedestrians and cyclists."
The failure to wear seatbelts was becoming a particular problem, he said. The number who died on the roads because they were not wearing belts had risen by 50 percent.
"Typically year-on-year about 60 people die in road crashes who are not wearing safety belts. Last year, in the last 12 months, that's gone up to over 90. Those are completely preventable deaths."
The provisional toll for the whole of 2016 is 327, eight more than in 2015 and 34 more than in 2014.