Two car crashes, one in Whanganui and one in Hāwera, led to seven people being taken to hospital with moderate and minor injuries.
Four people with minor injuries were taken to hospital after a car rolled in Whanganui.
Emergency services were notified of a single-car crash on Airport Rd just before 10pm on Wednesday.
A person was trapped and two children were involved in the crash, a Fire and Emergency spokesman said.
The passengers were two young mothers and two babies, aged 6 and 7 months old. They were checked at Whanganui Hospital and released later that night.