A 23-year-old man has been charged with murder after a newborn baby died in hospital following an incident in Perth's north.

Detectives from the child abuse and homicide squad are investigating what happened at a home in Innaloo more than three weeks ago.

Police say the eight week old was found with serious injuries on May 2. 

Residents said a neighbour performed CPR on the baby, who was described as being blue, until paramedics arrived. 

The baby died at Perth Children's Hospital two days ago.

A 23–year-old man was today charged with murder and remanded in custody until his next court appearance.