Three people are dead after three cars and a truck crashed south of Whangarei this morning.

Several others have critical injuries.

Northland Senior Sergeant Ian Row said the crash happened at Oakleigh at 11.15am.

Three people are believed to have died at the scene.

A St John spokeswoman they had also treated one person with moderate injuries and one with minor injuries.

SH1 is blocked between Mangapai Rd and Maungakaramea Rd and will be for several hours. Diversions are in place via Tauraroa Rd and police advise motorists to avoid the area completely if possible.

An Oakleigh resident who lives near the crash said she was not able to see the crash but traffic had built up past Mangapai Rd to the petrol station, about 1km away.

"It is a state highway so it is usually quite busy and when you get an incident the traffic builds up fairly quick," she said.

"The traffic was bad, but they are clearing it quite quickly."

The deaths have brought the road toll to 317 for the year so far, up 53 on the same time last year.

The first road death for November was a 37-year-old Dunedin man who died after
crashing into a power pole this morning.

Last month, 30 people died on New Zealand roads, including nine on the weekend of October 6-9 alone.

SH1 is blocked between Mangapai Rd and Maungakaramea Rd and will be for several hours. Diversions are in place via Tauraroa Rd and police advise motorists to avoid the area completely if possible.

Serious #Crash on SH1 in Oakleigh (btwn Oakleigh Rise & Mangapai Rd) - traffic control & detour will be in place #TakeExtraCare ^TY

— NZTA Akld & Nthlnd (@NZTAAkl) October 31, 2017