Hundreds of firefighters were battling a wildfire Thursday that spread from Oklahoma to Kansas and has burned an estimated 625 square miles. Two people have been treated for smoke inhalation.

About two-thirds of the burned land was in Kansas, according to preliminary estimates by the Oklahoma Forestry Services.

Fire officials in Barber County, where crews are working to extinguish a 30- to 40-mile line of fire, anticipate that the blaze will continue through Friday, said Darcy Golliher, a spokeswoman for the Kansas Incident Management Team. She expressed hope that there would be just a few hot spots to monitor over the weekend.

"It will all depend on the wind," she said.

The National Weather Service said 25 mph winds are forecast in the area until noon, when they are expected to drop to 15 mph and then to 10 mph by sunset. Gusts of 45 to 50 mph were reported Wednesday. Gov. Sam Brownback has declared a state of disaster emergency in some areas, authorizing state resources to assist.

In neighboring Comanche County, the fire that was briefly brought under control late Wednesday reignited the following morning, said John Lehman, Comanche County Emergency Management coordinator. Lehman said the blaze reignited when winds blew embers onto unburnt land.

"The wind blow things around," he said. "It hits dry grass and away it goes."

Golliher said the Kansas State Highway Patrol planned to fly over Thursday afternoon to evaluate the damage if the winds cooperate. The Oklahoma Forestry Services also was planning aerial surveillance.

The blaze went around the Barber County town of Medicine Lodge, where authorities say up to 1,000 structures were threatened and a voluntary evacuation order was issued, said Ben Bauman, director of public affairs for the Kansas Department of the Adjutant General. One home and outbuilding were destroyed on the outskirts of town. Voluntary evacuations also were ordered Wednesday in the small towns of Sun City and Lake City, which have a combined population of around 140.

Medicine Lodge Memorial Hospital was evacuated, sending 12 patients to a nursing home and two others to a nearby hospital. Authorities were making plans to return the patients Thursday.

Hospital CEO Kevin White said the smoke was so thick that it "completely obliterated the sun" at 5 p.m. Wednesday, an hour before the patients left. The hospital kept its emergency room open and treated one firefighter and one member of the public for smoke inhalation.

Meanwhile, four towns in Barber County, with a total population of 5,000 people, remain at risk Thursday if the winds shift, Golliher said.

The fire forced the closure of a stretch of U.S. 160 and U.S. 281 and scattered power outages have been reported.