The incident happened around 4:35 p.m. PT just after the horse participated in a cattle-penning event, said a statement issued by PNE spokeswoman Laura Ballance.
"The horse traveled into the Miller Drive area of the fairgrounds before being very quickly caught by PNE staff," said Ballance.
"One guest walked to First Aid and was then transported to Burnaby General Hospital. The other guest, when transported to Vancouver General Hospital, was awake and alert."
The horse was unharmed.
Ballance said the PNE staff were reviewing the incident to ensure it did not happen again.
The 15-day-long Pacific National Exhibition is non-profit event run by the city of Vancouver at Hastings Park every summer.