Police want to speak to a truck driver who avoided a crash shortly before a two-car collision closed State Highway 1 for hours.
Two people were critically injured and were flown to hospital.
Diversions were in place between Raumati Road and Poplar Avenue at Kāpiti, after the crash site at the Raumati off ramp shortly before 8am.
Police said they would like to hear from witnesses, including a truck driver who narrowly avoided a crash with a silver Volkswagen Golf on the old SH1 shortly before the crash.
SH1 was closed for hours, but has since reopened.