Two people are under arrest after the death of a two-year-old girl, police said.
Officers were called by the ambulance service at 11.44pm on Tuesday to a house on Jameson Street in Blackpool after a report that the toddler had suffered a cardiac arrest.
She was taken by ambulance to Blackpool Victoria Hospital but doctors could not save her. A post-mortem examination is due to be carried out to establish the cause of death.
Two women, aged 29 and 65, and two men, aged 41 and 60, all from Blackpool, were arrested on suspicion of child neglect.
The 29-year-old-woman and the 41-year-old man have now also been arrested on suspicion of manslaughter and attempting to pervert the course of justice. They remain in police custody where they continue to be questioned.
The other two have been released.
Detective Superintendent Paul Withers, of Lancashire Police, said: "This is a tragic incident where a little girl has lost her life.
"A full investigation is under way to try to establish exactly what has happened. Specially trained officers are offering support to the family."