The incident occurred just after 4:30 p.m., following a cattle-penning show inside the Livestock Barns.
The PNE says the horse got loose from its stall, travelled into the Miller Drive area of the fairgrounds and knocked down two guests.
It says one guest walked to First Aid and was taken to Burnaby General Hospital and the other guest was taken awake and alert to Vancouver General Hospital.
The fair says the horse was caught and was unharmed in the incident.
The annual fair was founded in 1910 and runs for 15 days at Hastings Park.
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