According to The Telegraph, the victim is believed to be just four years old.
The East of England Ambulance Service Trust (EEAST) said it received more than a dozen calls to the incident and several people, including the RNLI, came to the aid of the girl.
A post-mortem is due to take place into her death on Monday afternoon following the tragedy on Gorleston beach in Norfolk on Sunday morning.
"The young girl was taken to the James Paget Hospital; however sadly died".
"We would like to thank everyone who rushed to respond the young patient, and did everything possible to give her treatment and care".
"A parent myself, I can't imagine the grief being experienced by the family during this hard time".
Images of the scene show an area of the beach, with what appears to be crumpled canvas and abandoned deck chairs, cordoned off by police.
Cruise Worker Goes Overboard, Found by Another Cruise Ship
The US coast guard received reports of the overboard employee on Saturday afternoon and searched for him throughout the night. The crew member was seen falling overboard from the Norwegian Cruise Line Ship (pictured) on Saturday afternoon.
A witness said the contraption made of canvas and air exploded, propelling the girl 20 feet into the air.
We were called to a report of an inflatable trampoline apparently bursting on Gorleston beach, following a call to the ambulance service. "Never ever will I let my girls on a bouncy castle, ever".
The owner of Bounce About, Curt Johnson, 47, who wasn't present at the time of the incident, said the inflatable castle may have exploded in the heat.
After the incident, Robert Halfon, a member of parliament who represents the area, called for an "urgent investigation" into the regulation of inflatable trampolines.
Police and the Health and Safety Executive have confirmed they are leading a joint investigation into the girl's death.
Summer Grant was playing on the castle when it "cartwheeled" 300 metres down a hill with her still inside.
He said: "There should be a temporary ban on bouncy castles in public areas until we can ensure they are safe".