The Route Fire near the 5 Freeway at Castaic had burned 600 acres as of Wednesday afternoon with no containment, according to Los Angeles County Fire Department.
Officials said that evacuations have been ordered for the Paradise Mobile Home Park in the area.
Authorities say that the fire was initially reported near the freeway’s northbound lanes but quickly jumped across the road causing California Highway Patrol to close all lanes in both directions.
Traffic on the freeway, which connects San Francisco to Los Angeles, was backed up for miles, according to KTLA.
Los Angeles County Fire Department says that seven firefighters have heat-related injuries, with five taken to hospital as they battled the fire in temperatures of more than 105 degrees.
Firefighters were seen digging containment lines in the area while the fire was also fought from the air by helicopters and airplanes dumping retardant and water on the flames.
Officials say that the cause of the fire remains under investigation.
Southern California is currently in the grips of an extended heatwave that is expected to last until next week, with temperatures across the region hitting triple digits.
The region’s Inland Empire and desert areas are expected to see temperatures top 110 degrees Fahrenheit, while the state’s Death Valley could set a September record with a temperature of 126 degrees.
High temperatures could put stress on California’s electrical system, warned the state grid operator, as energy demands rise, largely due to air conditioning needs. Over the weekend, when temperatures are supposed to be hottest, electricity conservation may be necessary to avoid outages, they added.