The driver, the sole occupant, of one car died at the scene.
There were eight people in the other vehicle, five of whom received serious to moderate injuries, and were taken to hospital by ambulance.
Three other occupants had minor injuries, and were taken to hospital for medical assessment.
This came after a shocking Saturday afternoon of fatal crashes in Auckland and Waikato.
One person died in a two-vehicle collision in Māngere East, at the intersection of Massey and Bucklands Rds, about 6pm.
A member of the public at the scene told the Herald that one car was on its roof on Massey Rd and the other car was in the middle of the intersection.
About an hour and a half earlier, another person died after a two-vehicle collision on Mangatawhiri Rd.
Another person, a female, was injured in the crash and transported in a moderate condition to Middlemore Hospital.
Intensive care paramedic Chris Deacon described the scene when they arrived.
"It appears that it was a head-on collision on an open road," he said.
"One vehicle had left the road and was upturned. Its occupant unfortunately died despite emergency services attempts to save them."
He said local fire crew did an excellent job trying to revive them but were unsuccessful.
One person was also killed after a two-car crash in Karaka, Auckland, on Friday night.
Police were called to the crash on Karaka Rd, near Whangapouri and Blackbridge Rds, about 6.15pm.
One person died at the scene.