Firefighters trying to prevent an explosion in a tank of hazardous chemicals in Southern California found overnight that the failing tank was heating up internally despite efforts to cool it, the incident commander said on Saturday.

Southern California officials have expanded an evacuation zone in several Orange County cities over a toxic chemical tank that they say is "actively in crisis."

Southern California officials have expanded evacuations in several Orange County cities due to concerns over a leaking toxic chemical tank that they say is "actively in crisis."