A semi-truck carrying compressed hydrogen caught fire in Diamond Bar on Sunday afternoon, forcing hundreds of people in the area to evacuate, officials said.
The fire broke out about 1:20 p.m., when one or more of the 25 hydrogen cylinders on the truck began leaking, said Art Marrujo, a dispatch supervisor with the Los Angeles County Fire Department.
About 500 people near the intersection of Brea Canyon Road and Golden Springs Drive were evacuated as crews cooled the cylinders with water.
"We're going to let them [let off the] gas until everything's dissipated," Marrujo said.
Most of the evacuations occurred at nearby businesses. No injuries were reported.