The fire was quickly extinguished by crews using 2 hose reel jets and 4 breathing apparatus and they remained to cool 2 x 19kilogram propane cylinders.
The fire service have confirmed that the cylinders were outside the van and did not explode during this incident.
A fire investigation officer remained on scene to carry out investigations and will return tomorrow to continue further investigations into the the cause.
The van was all but destroyed receiving 80% damage.
The National Pony Society was holding a one-day event at the showground.
Two people inside the van received severe burns and were taken to Pinderfields Hospital, where they remain, while three people outside received minor injuries/ smoke inhalation and were taken to Harrogate Hospital.