A man has been charged with murder following the death of a four-week-old baby in Kaitāia.

Acting Detective Inspector Lloyd Schmid of Northland CIB announced a 22-year-old man was charged with Maree Takuira Mita Ngahere's murder this afternoon.

The man is due to appear in the Kaitāia District Court tomorrow and the man also faces a charge of assault on a child in relation to a separate matter.

Maree died on February 19, police reporting that her death was not accidental.

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Results from a post-mortem indicated she suffered a brain injury and bleeding to her brain. There was also severe bruising on one arm and thigh.

Her death was the second death of a child due to non-accidental injuries in Northland in eight months.

In August last year a 2-year-old died at a property in Mangawhai, resulting in a homicide investigation and charges being laid against a 30-year-old man.

The man, the victim and the child's mother were granted name suppression, along with any information that could identify them.

On average, a child in New Zealand is killed every five weeks, putting the country high on the list of the world's worst offenders, according to a 2016 report.

Sixty-one children died as a result of non-accidental injuries in New Zealand between 2006 and 2016.

The New Zealand Police Homicide Victims Report 2017, released late last year, showed 686 people were killed by homicide in New Zealand over that period, with children under the age of 5 making up 12 per cent of the victims.