Properties destroyed in Northern California fires

Wildfires burning in Northern California have scorched properties and forced thousands to evacuate, as hot, dry and windy conditions in the region challenge firefighting crews.

Officials said between 35 and 40 homes and other structures have burned in the fast-moving River Fire that broke out Wednesday near Colfax, a town of about 2,000.

Within hours it ripped through nearly 4 square miles (10 square kilometers) of dry brush and trees. There was no containment and about 6,000 people were under evacuation orders across Placer and Nevada counties, according to firefighting officials.

After firefighters made progress earlier in the week, red flag weather conditions of high heat, low humidity and gusty afternoon and evening winds erupted Wednesday and were expected to be a continued threat.

Winds were expected to change direction multiple times on Thursday, putting pressure on firefighters at sections of the fire that haven’t seen activity in several days, officials said.

Similar risky weather was expected across Southern California, where heat advisories and warnings were issued for interior valleys, mountains and deserts for much of the week.

Heat waves and historic drought tied to climate change have made wildfires harder to fight in America's West. Scientists say climate change has made the region much warmer and drier in the past 30 years and will continue to make weather more extreme and wildfires more frequent and destructive.

More than 20,000 firefighters and support personnel were battling 97 large, active wildfires covering 2,919 square miles (7,560 square kilometers) in 13 U.S. states, the National Interagency Fire Center said.