An 18-year-old woman was airlifted to Whanganui Hospital on Christmas Eve after a crash on SH4.
Five other people were taken to Whanganui Hospital by road ambulance.
The two-car crash happened near Otoko Marae, about 40km north of Whanganui, just before 12 noon on Sunday.
A spokeswoman for Whanganui Hospital on Tuesday said the airlifted woman, the most seriously injured of the six, was still in hospital in a stable condition. She is believed to have head and back injuries.
The other five people were treated and discharged.
The rescue helicopter was also called to assist in Mangaweka around 6pm on Christmas Day, after a 53-year-old woman fell from her bike and injured herself.
The woman was treated at the scene then flown to Palmerston North Hospital.
The woman suffered rib injuries, but her condition was not available on Tuesday.