Firefighters from Maungaturoto and Ruawai did mostly traffic control and the road was re-opened by 6am that day.
In January, a man from Paparoa was killed in a single-car crash on SH12 in Matakohe.
In the second crash, a woman was killed and another woman and two children were injured after their vehicle went off the road and ended on its roof. The injuries of the other people are unknown.
The accident happened on State Highway 10 in Kaingaroa in the Far North about 12.30pm on Saturday.
The section of highway where the crash occurred, between Zidich Rd and Duncan Rd, was down to one lane and police advised motorists to expect delays.
Deputy fire chief in Kaitaia, Craig Rogers, said the crash happened on a bend and the car appeared to be a write-off. Two fire appliances from Kaitaia responded.
The Police Serious Crash Unit is investigating both crashes.
Prior to the latest fatalities, two men died when they were thrown from a twin-cab ute when it rolled after a collision with another ute on State Highway 1 north of Ohaeawai about 10.20pm on May 13. Both were not wearing seatbelts.
They were Colin Risetto-Blade, 28, who had returned to Auckland about 10 days earlier after living in Australia, and Zion Harris-Davis, 23, from Auckland but with family links to Kaeo. It is understood they were in a group returning from a hunting trip at the time of the crash.
Mr Ewers estimates up to 40 per cent of fatalities were the result of people failing to use a seatbelt.
"The message is very simple - obey the road rules, don't speed, don't drink and drive and put your seatbelt on.
"Issuing tickets to drivers who don't follow road rules is not the answer. At the end of the day, the community has got to take safety messages on board," he said.
Northland's road toll last year was 27 while 22 people died in road crashes in the region in 2015.