(CNN) -- A days-long wildfire had covered more than 78,000 acres of Alaska's Kenai National Wildlife Refuge by early Saturday, a state agency said. The Funny River Fire began burning Monday evening and was 20% contained by early Saturday, Alaska's Interagency Incident Management Team said. No evacuations or injuries have been reported. There were more than 409 firefighters battling the blaze. Officials say access to the fire is difficult. Investigators suspect human action was the cause, but this is still under investigation. The refuge is in Soldotna, south of Anchorage. Kenai Peninsula Borough Spokesman Brad Nelson said there are two subdivisions in the area of the fire. The combined population of these localities is approximately 5,000 residents. What to know about wildfires .
NEW: Wildfire scorches nearly 80,000 acres in Alaska . NEW: Blaze was 20% contained by early Saturday . No evacuations or injuries have been reported .