A second person, a woman aged 38, also from Cefn Fforest, is currently receiving treatment in hospital
The girl was pronounced dead at the scene of the incident in Wheatley Place, Cefn Fforest, Blackwood, Gwent.
Police, including firearms officers, attended a property at around 7.15am on Thursday morning following reports two people had sustained serious injuries.
A second person, a woman aged 38 also from Cefn Fforest, is currently receiving treatment in hospital.
An 18-year-old man from Newbridge was arrested on suspicion of murder and attempted murder and remains in police custody.
Detective Superintendent Philip O’Connell, the senior investigating officer, said the family of the girl have been informed.
“We can confirm that we’re not looking for anyone else in connection with this incident after making this arrest earlier,” he said.
“We understand that reports of this nature can be concerning, and it is likely that residents will see an increased number of officers in the area while we carry out further inquiries.
“If anyone has any information, please speak to our officers or contact us in the usual way.”
