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The fire is burning just south of Lake Piru, a reservoir located in the Los Padres National Forest. It's close by Lake Castaic, a popular recreation area burned by the in January. That fire burned about 15 square miles (39 square kilometers) in six hours and put 50,000 people under evacuation orders or warnings.

In LA County, around 4,200 residents and 1,400 structures are under an evacuation order, and another 12,500 residents are under an evacuation warning, said spokesperson Andrew Dowd for the Venture County Fire Department.

The evacuation zones in nearby Ventura County are relatively unpopulated, Dowd said. Fifty-six people were evacuated from the Lake Piru recreation area.

Dowd said the fire was a “very dynamic situation� caused by hot, dry weather, steep and rugged terrain and dry fuel. There were 250 firefighters on the ground coordinating with helicopters and other air support, he said.

LA County Supervisor Kathryn Barger, who represents the district, urged residents to evacuate.

“Extreme heat and low humidity in our north county have created dangerous conditions where flames can spread with alarming speed," Barger said in a statement. “If first responders tell you to leave, go—without hesitation.�

The new blaze comes as a massive wildfire in Central California became the state's , threatening hundreds of homes and burning out of control in the Los Padres National Forest.

The Gifford Fire had spread to 154 square miles (399 square kilometers) by Thursday afternoon and was at 15% containment. It grew out of at least four smaller fires that erupted last Friday along State Route 166, forcing closures in both directions east of Santa Maria, a city of about 110,000 people. It has injured at least four people. The causes of the fires are under investigation.

will be elevated through the weekend across much of inland California as a heat wave gripping the area intensifies. August and September are typically the most dangerous months for wildfires in the state.

“In Southern California, the threat is driven by persistent drought, high grass loads, and weakening coastal moisture,� according to a wildfire forecast by the state's fire department.