Helicopter pilot Lance Burns said they were dispatched to Taihape on Sunday morning for a young man who had inhaled fumes from a fire extinguisher.
"I heard it was some sort of prank," Mr Burns said.
St John Ruapehu territory manager Mark Fredericks said they received a call-out to a man about 16 minutes out of Taihape, who was having difficulty breathing "as a result of a fire extinguisher going off in his face".
It is not known if the man remained in hospital.
Wanganui fire Senior Station Officer Gary Wilson warned people to use fire extinguishers only for putting out fires and not aim them at people or animals.
"There's a number of types out there. The main ones are dry powder, which is basically baking soda and CO2, which is carbon dioxide," Mr Wilson said.
"They are all stored under pressure. Just the pressure alone would endanger somebody's health.
"They are designed to work away from the body, of course.
"Like anything, they're a tool not a toy."