Two people were taken to hospital with critical injuries after the car they were travelling in lost control and crashed into a creek in Dargaville.
Police were alerted to the single-vehicle crash on State Highway 12 at 2.50pm on Saturday.
Analyst Jeff Cramp of Northland Serious Crash Unit said one male and one female, aged in their 20s, were heading north from Dargaville when the male driver allegedly lost control while attempting a right-hand bend.
Police were investigating whether speed was a factor in the crash.
“What we do know is that neither of the vehicle occupants had a seatbelt on and could have prevented much harm to themselves if they just followed the road rules,” Cramp said.