Wildfire update: Crews make slow progress against sprawling California blazes

Lightning-sparked wildfires in Northern California have spread to become some of the largest in state history, forcing thousands to flee and destroying hundreds of homes and other structures as reinforcements began arriving to help weary firefighters.

At least 100,000 people are under evacuation orders. Fire crews made slow progress Saturday battling some of the largest wildfires in California history — thanks to improved weather conditions and additional resources coming from others states.

But danger loomed with the threat of thunderstorms and lightning forecast for Sunday that could spark new fires and overwhelm firefighters battling hundreds of fires throughout the state.

"The worst is not behind us, we are in a battle rhythm," California Department of Forestry and Fire Protection Chief Thom Porter tweeted.

Light winds, cooler and more humid nighttime weather and more equipment arriving for firefighters helped them make their most significant progress battling three massive Northern California fire "complexes" -- multiple wildfires in one area being treated as a single incident. They have burned 1,045 square miles (2,700 square kilometers).

The fires that started this week have killed five people, destroyed nearly 700 homes and other structures and forced tens of thousands from their houses.