The site was hosting the Family Funfair run by Kent-based Forrest Amusements which, according to a poster, was due to open to the public on Wednesday.
The Health and Safety Executive (HSE) is investigating the circumstances of the incident, which Kent Police said was “not suspicious”.
A South East Coast Ambulance Service spokesman said: “We were called at 7.42am this morning to a serious incident at Pencester Gardens in Dover.
“We immediately dispatched a number of clinical resources to the scene, including our Hart team and critical care paramedics; however, sadly, a teenage boy was pronounced as deceased at the scene.”
A Kent Police spokesman said: “Kent Police was called by South East Coast Ambulance Service to Pencester Gardens, Dover, at 7.45am on Wednesday 3 August 2022.
“No suspicious circumstances have been reported, and the Health and Safety Executive have been informed.”
An HSE spokesperson said: “HSE is assisting emergency services with their response.”