The woman said members of the public were directing traffic and a number of people had pulled over to help.
The Serious Crash Unit is investigating.
The incident brings the holiday road toll to four.
Two people were killed when a bus crashed near Gisborne on Christmas Eve.
Sione Taumalolo, and Talita Moimoi, understood to be a 12-year-old boy and a 20-year-old woman respectively, were killed when their bus crashed down a 100 metre bank.
Taumalolo is understood to be a student at Mailefihi Siuʻilikutapu College, whose brass band were touring New Zealand as part of a fundraiser.
Moimoi, who was chaperoning the school group when the crash occurred, is understood to be married and the mother of a young daughter.
An elderly woman also died after being hit by a car in Takapuna, on Auckland's North Shore on Friday.
The official holiday road period began at 4pm on Friday and runs until 6am on Wednesday, January 4. Last year's Christmas road toll was 12, from 244 reported injury crashes.