A woman has been arrested after a child was found dead at a property in Trealaw.
The 37-year-old was detained when emergency services were called to an address in the town at about 22:20 BST on Friday.
South Wales Police has not given the age or gender of the child but said the death is being treated as unexplained.
The nature of the allegation against the woman, who is being held at Merthyr Tydfil station, is also unknown.
As part of the investigation, the main route through Trealaw, Brithweunydd Road, has been closed off.