The incident happened near the intersection of Golden Springs Drive and Brea Canyon Road, as the big rig was hauling 20 individual 50-gallon tanks filled with hydrogen, according to the Los Angeles County Fire Department.
Firefighters responded to the scene and doused the vehicle with water as sheriff's deputies closed the street. A hazardous materials team was also summoned to the location.
About 500 people were evacuated from surrounding businesses.
There were no immediate reports of injuries.
DEVELOPING: More details will be added to this report as they become available.