Rising temperatures pose new challenges for firefighters who have made incremental progress against a massive wildfire in central California that has injured four people as it has become the biggest blaze in the state so far this year.

The Gifford Fire burning through the rugged backcountry of California's Central Coast is now the state's largest wildfire of the year. It has reached so-called "mega-fire" status and is one of 38 large fires burning across nine states.