A Department of Fire and Emergency Services (DFES) spokeswoman said about 70 firefighters were needed to control the blaze, which continued to intensify after it was first reported in dunes near Marmion Avenue and Roundhouse Parade just before 4pm.
Residents who lived in the area were put on alert as aircrews water-bombed the flames, which flared in problematic winds.
Ambulance crews were called to the scene about 4.20pm after four vehicles crashed into each other near Marmion and Benenden avenues.
A St John Ambulance spokesman said two people were taken to Joondalup Health Campus under non-priority conditions.
The department declared the fire, which burned about 8ha of bush, no longer a risk to homes just after 6pm, but were still warning residents to be cautious because of smoke in the area on Friday morning.
A DFES spokeswoman said the fire was suspicious. The land is believed to be owned by a developer.