Mandurah fire crews are at the scene of a fire in Dudley Park near Mandurah Catholic College.
A blaze was reported about 4.12pm in a unit on Mariners Cove Drive near the intersection with Heyerdahl Way.
It is understood four people were in the unit when the fire erupted, including a couple and two younger children.
One man is being treated at the scene for smoke inhalation. He is also believed to have received minor burns.
The fire was brought under control about 4.35pm and was contained to a single room in the apartment, but the rest of the property has been damaged by smoke.
Two fire crews, ambulances and police were on the scene.
It is unclear what caused the fire.
Police will continue to investigate.