A woman has been arrested on suspicion of murder after an 18-month-old baby fell from a sixth-floor window and died.
Officers were called to Barkerend Road, in Bradford, yesterday at about 5.10pm following a report a child had sustained life-threatening injuries.
West Yorkshire Police said it quickly became apparent the baby boy had died.
Detective Superintendent Nick Wallen, who is leading the investigation, said: "This is clearly an extremely traumatic incident and specially trained officers are working to support the child's family members and those who witnessed what took place.
"It is no exaggeration to say those who witnessed this incident will have been deeply traumatised by what they saw.
"A 23-year-old woman has been arrested on suspicion of murder in connection with the baby's fall and she is currently receiving medical assessment in custody."
Police said they are not looking for anyone else in connection with the incident but have appealed for witnesses or anyone with information to come forward.
A crime scene remains in place at the scene as inquiries continue.
Anyone with any information is asked to call Bradford CID on 101, quoting reference number 1506 of October 21.