Following allegations of a dog attack, officers from Gwent Police were dispatched to an address in Pentwyn, Penyrhoel, Caerphilly at around 3.55pm on Monday.
The event was attended by specially trained firearms police and paramedics from the Welsh Ambulance Service.
Unfortunately, a 10-year-old boy died on the spot.
According to police, the dog was killed by firearms officers, and no additional animals were involved in the incident.
"Officers will be making further inquiries at this time and will stay at the scene as the investigation proceeds," Chief Superintendent Mark Hobrough said.
"As part of this effort, you might notice continued police activity in Caerphilly." Please do not be worried if you noticed an increased presence earlier today when officers were responding to the incident.
"Please stop and speak with us if you have any issues or information."
Anyone with information can contact Gwent Police on 101 and reference log reference 2100392510.
Alternatively, you can ring Crimestoppers to remain anonymous at 0800 555 111.