A brush fire in a mountainous area north of Los Angeles ignited and spread quickly Thursday, forcing thousands of evacuations.

The Canyon Fire ignited around 1:30 p.m., growing to over 1.6 square miles (4.1 square kilometers) in less than three hours, according to Ventura County emergency response. It remained zero percent contained late Thursday afternoon and was spreading east, the county said.

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 Hughes Fire 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.

The new blaze comes as a massive wildfire in Central California became the state's largest blaze of the year, 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 has injured at least four people. The causes of the fires are under investigation.

Wildfire risk 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.