An explosive brush fire raced through Southern California with ferocious speed Tuesday, spreading from about 50 acres to an estimated 31,000 acres in a matter of hours, forcing thousands of residents to flee and leaving at least one person dead.

Named the Thomas Fire, it began in a canyon near Santa Paula, about 65 miles northwest of downtown Los Angeles. By 4 a.m. Pacific time, the fire had advanced into the city limits of Ventura, with a population of more than 100,000, emergency officials said.