A fire has broken out at the border of Los Angeles and Ventura counties and is spreading rapidly, threatening numerous hillside homes in the Calabasas and Hidden Hills areas.

UPDATE Jan. 9, 8:35 p.m. The Kenneth Fire that erupted Thursday afternoon on the border between Los Angeles and Ventura counties is reportedly being investigated as an arson case, with one person in custody. As of Thursday evening, the blaze has expanded to 960 acres, with no containment.

By 3:25 p.m., Cal Fire said the fire had already spread to 50 acres. Evacuations were ordered in the Hidden Hills area, from Vanowen south to Burbank

Police have detained a suspect allegedly responsible for starting one of the fires raging in Los Angeles. The suspect is a homeless man in his 30s, according to Fox LA's Elex Michaelson. The suspect was initially detained "by citizens" in the Woodland Hills neighborhood not long after the Kenneth fire started on Thursday,

An arson suspect was arrested Thursday night near the Kenneth Fire area as fire crews continue battling flames burning near homes in Calabasas and West Hills. At around 4:30 p.m., Los Angeles police responded to reports of a man attempting to light a fire in the 21700 block of Ybarra Road in Woodland Hills.