Cleveland Police have arrested a 25-year-old woman and a 21-year-old man after concerns were raised about a two-year-old girl who later died in hospital, the force said.
Officers were called to Hartington Close in Thornaby, on Teesside, at about 16:20 BST on Saturday after reports about the child. The girl was taken from the area to hospital, where she subsequently died.
A Cleveland Police spokesperson said the pair were arrested "in connection with the child's death" and are being held for questioning. The force said the death is "currently being treated as unexplained" and that officers had launched an investigation.
"Our thoughts are with the family of the child during this very difficult time," the spokesperson added. Crime scene investigators were still at Hartington Close on Sunday, and there remained a visible police presence in the area.
Police did not provide further details about the circumstances that led to the child's death or whether any formal charges were expected. Investigations of this type typically involve forensic examination of the scene and inquiries with witnesses, the force said.
Thornaby is part of the Teesside area in northeast England. Local residents reported a sustained police presence on Sunday, but police have not issued a public appeal for witnesses or released additional information about the individuals arrested.
The investigation is ongoing and police said further updates would be provided as inquiries progress.