Two people have been arrested on suspicion of murder following the death of a two-month-old baby girl, police said.
Officers were called to an address in Sunnyside Road in Poole, Dorset, at about 7.20am on Saturday following a report from the ambulance service that the baby was not breathing.
The baby girl was taken to hospital, where she was pronounced dead.
Her death is currently being treated as unexplained and an investigation has been launched into the circumstances surrounding it.
Detective Inspector Richard Dixey, of Dorset Police's Major Crime Investigation Team, said: "Every child who dies suddenly has the right to have their unexplained death fully investigated so the cause can be identified.
"We are currently carrying out a range of enquiries in order to establish the full circumstances surrounding the very tragic death of this baby girl.
"I would ask that her family is given privacy at this extremely difficult time."
Police have been liaising with the coroner.
Investigations have included an examination of the scene and house-to-house enquiries in the area.
A 28-year-old man and a 30-year-old woman, both from Poole, have been arrested on suspicion of murder.
They have been released under investigation while police enquiries continue.
A post-mortem examination was carried out on Tuesday, with the cause of death remaining unascertained pending further tests.