The blaze, dubbed the Woolsey Fire, started in Simi Valley near the Rocketdyne facility in the Santa Susana Pass.
WATCH: Dramatic video shows flames crossing 101 Freeway in Santa Rosa Valley
By early Friday morning, the fire had grown to more than 7,500 acres with 0 percent containment. Multiple fire agencies responded to assist in battling the blaze.
At least 30,000 people were forced to evacuate just for the Woolsey Fire, authorities said.
Ventura County fire officials issued mandatory evacuation orders for Oak Park, Thousand Oaks residents from Thousand Oaks Boulevard to Sunset Hills, from Oak Park west to Highway 23, and Bell Canyon and Saddlebow Road between Maverick Lane and Morgan Road.
Voluntary evacuations were issued for Westlake Village, Agoura Hills, Calabasas and Hidden Hills.
The city of Calabasas tweeted that mandatory evacuation orders were issued for areas north of the 101 Freeway from Valley Circle Boulevard to Lindero Canyon Road. A voluntary evacuation order was in effect for areas south of the 101 Freeway.
A second fire burning in the Santa Rosa Valley east of Camarillo, west of Simi Valley near Newbury Park and Thousand Oaks, was mere miles from the scene of a deadly mass shooting that claimed 12 lives Wednesday night.
Ventura County fire authorities estimated the size of the blaze at upwards of 15,000 acres, but then officials downgraded the blaze to about 7,000 acres. Cal Fire tweeted that the blaze was about 10,000 acres.
Structures could be seen burning from the air as a line of flames closed in on a large residential area near Old Conejo Road.
Oak Park neighborhood evacuates as Woolsey Fire flames lap at homes
Mandatory evacuations were issued for Cal State Channel Islands, Vallecito Mobile Home Park and the Camarillo Springs and Dos Vientos areas, authorities said. Point Magu Naval Base was under voluntary evacuation orders.
Fire officials estimated that 1,200 homes were evacuated in the Camarillo Springs and Dos Vientos areas.
MORE: Full list of evacuations, road closures in Ventura County fires
The 101 Freeway was under full closure from Borchard Road to Pleasant Valley Road in both directions.
Ventura County Fire PIO provides update on Woolsey Fire
Hundreds of Ventura County firefighters and eight air tankers were battling the flames on the ground and from above.
Plumes of thick, white smoke could be seen rising above the burn site as strong Santa Ana winds drove the flames amid red flag conditions.
The cause of the fires remain under investigation.