Firefighters extended their containment of the 29-square-mile Sleeper Lake fire Sunday to 50 percent in the remote, marshy eastern Upper Peninsula, using helicopters to start backburns in one danger area.
But officials warned that an expected shift in winds threatened to give the blaze fresh life. The fire did manage to jump the fire line in a few small areas, but firefighters blocked any wide breakout.
The containment was an improvement from 25 percent Friday, the Michigan Department of Natural Resources said.
Some overly confident residents were making unauthorized efforts to return to their evacuated homes, an unwanted distraction for some fire crews, a state spokeswoman said.
"Folks are showing up out there," said Ada Takacs of the DNR. "That ties up our crews. They're not able to fight fire when they're doing it."
Some evacuees may not realize that reports of a fire being 50 percent contained mean only that half the fire's perimeter is under control -- not that the fire is half out, she said.
Firefighters have been able to bulldoze a line around most of the fire, but "not all of that line has been tested," the Takacs said.
The greatest concern for the fire's spread is in the northwest corner, near McMahon Lake and a few miles southeast of Pine Stump Junction, Takacs said. She said crews were starting back burns to clear out fuel between the bulldozer line and the main blaze.
Firefighters used an aerial "heli-torch" to start controlled burns Sunday.
A lightning strike is suspected of starting the wildfire Aug. 2 in Luce County, about 55 miles west of Sault Ste. Marie and about 300 miles north of Detroit.
It has been spreading through a mainly swampy portion of the Lake Superior State Forest, aided by dry conditions, gusty winds and hot weather.
Gov. Jennifer Granholm toured the fire's perimeter by helicopter Friday and said she would seek a federal disaster declaration for the area.
About 230 people from a variety of Michigan, Minnesota, Wisconsin, Ontario and U.S. government agencies were involved in the fight Sunday, the DNR said. The American Red Cross and other private agencies also were assisting.
"Firefighters continue to construct (a) line around the fire with 'dozers, plows, hand crews and water drops from the helicopters," the agency said in a statement Sunday.
So far, no one has been seriously hurt in the fire, Takacs said. Two firefighters were treated for dehydration, and a third twisted an ankle.
Once the fire is fully controlled, firefighters will begin the long, unpredictable process of making sure it is extinguished, Takacs said. That is particularly challenging in boggy areas, where combustible underground material can burn for days, weeks or months.