Police say there are multiple fatalities after a crash between a truck and a car on State Highway 1, near Kuku in Horowhenua.
The crash was reported to police just after 3pm.
Motorists were being asked to avoid the area.
Police have not yet been able to confirm the number of dead and injured.
The northbound lane of the highway,near the intersection of Kuku East Road, was expected to reopen shortly, police said after 7pm.
The southbound land had been reopened by that point.
Horowhenua mayor Bernie Wanden said the stretch of State Highway 1 between Levin and Ōtaki was notorious and dangerous.
The road has a history of being one of the most unsafe sections of highway and had a history of tragic crashes, he said.