A police statement said: “Kent Police was called at 3.13pm on Saturday 28 July to concerns for a girl in the sea at Margate Harbour.
“Officers and the South East Coast Ambulance Service attended the scene and the six-year-old from Erith was taken to hospital, where she later died.
“Her next of kin have been informed. There are no suspicious circumstances and a report is being prepared for the coroner.”
Beachgoers in Margate reported seeing multiple emergency service vehicles at about 3.30pm on Saturday afternoon.
One witness told Kent Live she saw police run onto the sands after hearing sirens.