Firefighters attended the scene at Park Holidays, in Ivyhouse Lane, Guestling at around 12.45pm on Saturday (July 30).
East Sussex Fire and Rescue Service (ESFRS) said six appliances were sent to the holiday park initially and advised people to avoid the area.
The ambulance service also sent paramedics.
At the height of the incident, crews from eight fire stations were there for several hours tackling the blaze.
An ESFRS spokesperson said: “Crews were called to a fire in a lower ground floor roof at Park Holidays, Guestling, at 10:55 on Saturday, July 30.
“At the height of the incident nine appliances with crews, from The Ridge, Bohemia Road, Battle, Bexhill, Rye, Broad Oak, Herstmonceux and Lewes, along with an aerial ladder appliance and a water carrier, used breathing apparatus, hose reels and 1in7 foam to tackle the fire, which was well alight on arrival.
“The fire was particularly hazardous as crews, working in warm conditions and with the potential for part of the structure to collapse, fought to prevent the fire from spreading to a nearby cleaning chemical and bedding storage facility.
“Despite despite severe damage to the roof crews were able to prevent the fire from spreading to other parts of the building and its annexes.
“Crews left the scene at 6.48pm having dealt with this challenging incident.
“There were no casualties. An investigation into the cause of the fire is ongoing.”