Police have launched a homicide inquiry following the death of a three-month-old baby girl in Porirua.

The baby died last week and an autopsy had revealed the girl had died from "non-accidental injuries" on November 13, Detective Senior Sergeant Kevan Verry said.

A Porirua man, 22, will appear in court today facing one charge of male assaults female and assault on a child.

"The investigation is still ongoing and police are working closely with the family of the deceased to ascertain further facts," Verry said.

"This is a tragedy impacting on a large family group.

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"Police are committed to supporting the family and providing answers to them."