Twin wildfires are ablaze across hundreds of acres in Ventura County north of Los Angeles and evacuations have been ordered in the region, according to reports.

One blaze, named the Lime fire, is burning across 450 acres close to Lake Piru in a hilly and forested area north of the town of Santa Clarita.

The Ventura County Fire Department said on Thursday morning that the blaze was 20 per cent contained but did not have a timeline for getting it under control.

Authorities have ordered mandatory evacuations of lands and campgrounds near Lake Piru with some 25 structures, including residential homes, threatened.

Some 250 firefighters were on the scene and building containment lines as aircraft dropped retardant on the flames.

Another blaze around 25 miles away, the Elizabeth fire, has been burning in the same region for close to 24 hours.

It has raced across 275 acres and is currently 70 per cent contained. Some 135 fire crew personnel were on the ground.

Two firefighters from the Elizabeth fire were taken from the front-lines suffering from exhaustion.

A rare occurrence of the strong and dry Santa Ana winds earlier this week have exacerbated fire weather conditions in the area. The National Weather Service on Thursday forecast "briefly critical" hot, very dry and breezy conditions for southwestern California.

Associated Press contributed to this report

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