A homicide inquiry is underway after the death of a child in the Bay of Plenty.

Police were advised on Saturday night that a five-year-old child had passed away at Rotorua Hospital.

"Police and ESR subsequently attended a Union Street address to make inquiries into circumstances surrounding the cause of the child's death," says a police spokesperson.

"A post-mortem examination is underway.

"A 24-year-old man has been charged with assaulting a child and appeared in the Rotorua District Court today."

He was remanded in custody to reappear on March 3.

Further charges are likely, says police.