A serious chemical leak accident forced the evacuation of more than 100 homes California's Perris city and also closed the 215 Freeway in both directions.
Perris is located 122 km east of Los Angeles, reports Xinhua news agency.
Local NBC 4 news channel reported that Cal Fire Riverside County received a call about the chemical leak around 7.40 p.m. on Thursday, when someone discovered a large plume of smoke coming from a rail car along the railway running parallel to the freeway in the town with over 77,000 residents.
Officials identified the leaking chemical as styrene, saying some kind of chemical reaction inside the tank occurred when the chemical used in latex, synthetic rubber and polystyrene resins was stored in an overheating situation.
Typically, styrene sits at around 29.4 degrees Celsius, but the roughly 188,000 pounds of styrene in the tank had reached temperatures up to 161.7 degrees Celsius, Cal Fire Riverside County Chief John Crater told reporters on Friday.
As pressure rose in the full tank and the styrene continued to heat up, there could be an explosion, Cal Fire Riverside County said, adding that firefighters could not approach the site and the styrene was still leaking from the top portion of the tank as of Friday.
Crater said he had spoke with experts across the country about potential impacts of the leak, adding "what they're telling me is this can resolve itself in two days".