UPDATE:Hannah Bonser, 26, was tonight charged with the murder of Casey-Lyanne Kearney who died after being stabbed in Doncaster, South Yorkshire Police said.
A woman was being questioned by detectives on Wednesday following the fatal stabbing of a 13-year-old girl, named as Casey-Lyanne Kearney.
The teenager, described by police as 5ft 3in with long, straight, ginger hair, collapsed at the scene and died hours later at Doncaster Royal Infirmary.
South Yorkshire Police have launched a murder inquiry.
A 26-year-old woman has been arrested and remains in police custody, a spokesman said.
Speaking near the scene, senior investigating officer Detective Superintendent Terry Mann said Casey-Lyanne had left her home at around midday yesterday, intending to catch the bus to Doncaster town centre where she was then going to meet a friend.
He said: "We believe that she then got off somewhere around this area here, and the next part we know is that, at 18 minutes past one yesterday, a call is received via South Yorkshire Police switchboard from Casey herself to say that she had been stabbed.
"At the same time, a passing member of the public has come by Casey and contacted an ambulance. In a very short period of time both police and paramedics arrived at the park area."
A police tent in Elmfield Park, Doncaster where a murder investigation is under way
The whole park remained sealed off today and blue police tape was attached to railings and trees.
Police community support officers were positioned at various locations.
A white forensic police tent could be seen in the park - just a few metres from a play area.
Locals spoke of their shock at hearing reports that the girl had been stabbed.
One woman, who was passing the scene with her 13-year-old daughter, said she no longer allowed her to go into the park.
"It is not a very good park, to be honest. There have been a number of incidents in there, it is not like when I was a child."
She said her daughter had come across a drunk woman when she was walking close to the park yesterday afternoon.
A police car at Elmfield Park, Doncaster where a murder investigation is under way
The teenager said: "We were just walking and we decided to run. She was walking past and she asked us why we are running. She started calling us names."
A local shopkeeper, who gave his name as Raja, said: "They should put CCTV cameras in the park. A few customers have been saying that."
He added: "It is such a shock. It is really sad. You see kids playing football in the park. It is the first time we have had a stabbing around here."
He said five or six years ago a man set himself alight in the park.
Doncaster Council confirmed the person in custody was "known to a number of local public agencies".
A police officer in Elmfield Park, Doncaster
Chief executive Jo Miller said: "We are deeply saddened by this tragic event and our thoughts are very much with family and friends.
"This incident is in the very early stages of a police-led murder investigation and we would urge anyone with any information to come forward and talk to the police. We can confirm that we are all working hard to piece together what happened yesterday and also gathering any information we can.
"The person in custody was known to a number of local public agencies and we are working together to establish all the circumstances involved with this case."
She said the investigation was at an early stage and any member of the pubic who has any information should come forward.