According to reports, the firefighters are combating excessive heat.

The Oak Fire has now burned 15,603 acres of land and is still "zero per cent uncontained", California's fire department said on Sunday night, BBC reported.

But it added that the fire activity is not as extreme as previous days, and firefighters are making progress, the British media reported.

So far, over 6,000 people have been evacuated.

A further 3,271 structures - both homes and businesses - are under threat, the California Department of Forestry and Fire Protection (Cal Fire) reported as quoted by BBC.

The blaze started on Friday.