Police have revealed a nine-year-old boy was killed in a crash in Canterbury's Ashburton Lakes region on Sunday.

Emergency services responded to reports of a car crashing into the Clyde riverbed near Erewhon Station Hut about 10am.

Police say two other people had moderate and minor injuries.

The Serious Crash Unit has examined the scene - and police say the investigation is ongoing.

One person also died in a car crash near Oakleigh, Northland, yesterday afternoon. Three cars collided on State Highway One between Mangapai and Whangarei, with several having to be rescued from their cars by emergency services.

One person received serious injuries, and another moderate.