Police say two 19 year olds accused of harming a young child who later died will face new charges when they appear in court on Friday.

The child was taken to hospital in a critical condition after emergency services were called to a property in Otautau in Southland on Sunday night.

They were flown to Starship Children's Hospital in Auckland where they died on Wednesday afternoon.

The 19 year olds were charged with causing grievous bodily harm and remanded in custody after  on Monday.

Police have not said what the new charges are.