A seven-year-old girl has died after being stabbed by a stranger in a park.
The girl suffered serious injuries in the attack at Queen's Park in Bolton at about 14:30 GMT, Greater Manchester Police said.
A force spokesman said despite the "best efforts of her family and medical responders, she died a short while later".
A 30-year-old woman, who was not known to the family, was arrested at the scene on suspicion of murder.
Assistant Chief Constable Russ Jackson said officers were "working to understand the motive for this completely random and brutal attack".
"A woman who was not known to the family was detained by a member of the public and then arrested by the police," he said.
"We understand that the woman has some history of mental illness and we are working to understand if this played any part in her motive."
He said the attack was "a family's worst nightmare".
"The incident is horrendous and I cannot begin to imagine what the family of this little girl are going through," Mr Jackson said.
"We are determined to quickly understand how this came to happen, leaving a young family so distraught and so devastated in an instant."