Officers are treating the child’s death as unexplained and are awaiting results from a postmortem to establish the cause of death.
The ambulance service was contacted at about 9.40pm on Monday, after the young girl was reported to be unresponsive, at the Cala Gran holiday park in Fleetwood, Lancashire.
A spokesperson for Lancashire police said: “The ambulance service contacted police after a 12-year-old girl was found unresponsive at the scene by paramedics. The girl was taken to Blackpool Victoria hospital for treatment but sadly died a short time later.”
No arrests have been made.
A spokesman for Cala Gran holiday park said: “This is a tragic incident, and our heartfelt condolences go to the girl’s family, who we have offered our support to.”