The Funny River Fire threatens about 150 cabins, vacation homes and year-round residences in three communities. Authorities have told people in those areas to be ready to leave but had not issued an evacuation order.
The fire, named after a road near its northern edge, was burning in the 1.9 million-acre Kenai National Wildlife Refuge and grew by about 42 square miles on Saturday but did not get any closer to structures. No buildings have been damaged and no injuries have been reported.
The size of the blaze is not unusual for Alaska but the state does not usually see such large fires this early in the season, said Michelle Weston, spokeswoman with the Alaska Interagency Management Team, which includes the state Division of Forestry and federal and local officials.
For size comparison, as of Sunday morning, the Funny River Fire was larger than Seattle (143 square miles) but smaller than Anchorage (1,961 square miles).
The Alaska Department Natural Resources warned residents of Anchorage, the state's largest city, to expect to see considerable smoke from this and another wildfire.
About 450 firefighters are assigned to the Funny River Fire, which is the most active of several large wildfires burning in Alaska. Firefighters have been flown in from Oregon, Montana and Canada to help Alaskan crews.
They were working Sunday to build and strengthen containment lines on the west and north perimeters of the blaze, fire spokesman Bernie Pineda said. They hope to complete the west line within the next few days, he said.
"We had a great day fighting the fire yesterday," Pineda said, adding that the lines crews had built earlier held well despite strong winds.
Fire officials said they were expecting some rain by Tuesday and predicted the warnings for possible evacuation of the threatened homes could be lifted sometime Monday.
Gov. Sean Parnell flew over the fire midday Sunday. He praised the multiagency effort including state, local and federal officials.
"Lots of pieces are working well together right now," Parnell said during a news conference. "Thanks so much to the entire team for keeping Alaskans safe."
Wildfires in Alaska's remote areas are not unusual during the summer months, with an average of a million acres burned each fire season, Weston said.
The state is experiencing unusually dry conditions because of unseasonably warm spring temperatures. High wind is also a challenge for crews.
The Kenai National Wildlife Refuge was established in 1941 as the Kenai National Moose Range and was aimed at moose protection. Wildlife viewing, fishing, camping and hiking attract visitors from around the world.