The large blaze was initially reported at 12:45 a.m. along a large encampment under a Sacramento light rail overpass near Interstate 80, Sacramento Fire Department Capt. Keith Wade told Fox News.
A massive plume of smoke could be seen from the freeway. Footage of the aftermath taken by KCRA-TV showed several larges tires burned and multiple vehicles charred underneath the overpass where the heat caused chunks of concrete to fall.
The blaze appeared to have traveled up an embankment and burned some vegetation.
Around 36 firefighters responded to the scene. They were told a female took herself to a hospital but her injuries were not clear, Wade said. No other injuries were reported.
Two bridges were damaged and light rail traffic was briefly suspended. Engineers walked the rails and deemed them safe for the morning commute but are expected to check for long-term damage, according to the news outlet.
Fox News has reached out to the California Department of Transportation.
One person told the news outlet that at least 40 people were displaced from the encampment.