The blaze broke out in the 27900 block of Baker Canyon Road near Blackstar Canyon Road just after 10 a.m.
Orange County Fire Authority officials said the fire started in a nursery in a mulch patch and spread into wild vegetation.
As of 11:30 p.m., the fire had burned 50 acres and was 25 percent contained.
Six homes were under voluntary evacuation orders on Baker Canyon Road.
A Red Cross evacuation center was set up at El Modena High School, 3920 E. Spring Street in Orange.
Crews from OCFA, USFS, Cal Fire and other Orange County fire departments were on scene.
The fire is located in the rugged Santa Ana Mountains a mile from the corner of Santiago Canyon and Silverado Canyon roads.
CNS contributed to this report.