An injured baby admitted to Wellington Hospital on Sunday is now in a critical condition.
Lower Hutt police say the 10-week-old boy was taken to hospital by ambulance early on Sunday with bruising and a possible head injury.
Police were notified shortly afterwards and began investigating the cause of the injuries.
A man, 28, is to appear in Lower Hutt District Court on Thursday.
Detective Sergeant Scott Cooper would not confirm the relationship between the man and the baby, other than to say that the man is a family member.
A Wellington Hospital spokesperson said on Tuesday the baby boy's condition had deteriorated, and he is now in a critical condition.