Rising temperatures on Wednesday posed new challenges for firefighters who have made incremental progress against a massive wildfire in central California that injured four people as it became 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.