Columbia, N.C. — For the second time in a week, dozens of Hyde County residents have been forced to flee their homes as a wildfire continues to spread in eastern North Carolina.

Area wheat farmers also hurriedly harvested their fields, fearing embers from the fires could send their crop up in flames.

The fire, which lightning sparked June 1, had burned 40,195 acres – about 63 square miles – in Hyde, Tyrrell and Washington counties by early Wednesday, authorities said. It has become the largest wildfire in North Carolina in more than 20 years and is the largest fire now burning in the U.S., they said.

Much of the area charred by the fire is in the Pocosin Lakes National Wildlife Refuge, and the dense woods and thick smoke have made it difficult for firefighters to locate hot spots. Helicopters have been dumping water over the area to help douse the flames.

Hyde County wheat farmer Martin Gelderman said the fire is approaching his fields from two sides.

"The size of it is amazing," Gelderman said. "We're getting (the wheat) off in case there's any danger."

The fire was 40 percent contained Wednesday morning, but shifting winds were pushing the fire back to the west after days of eastward-moving flames, authorities said. Fire crews have had to re-establish containment lines to the west and build new ones, authorities said.

They ordered 50 homes in the Waterway Landing community near New Lake evacuated late Tuesday because of the shift in the fire's movement. Residents were first forced from their homes late last week, but were allowed to return home as the fire moved east.

Jody Brady, of the state Division of Forest Resources, said smoke from the fire had carried as far as Norfolk, Va., by Tuesday, but the wind shift could bring more low-level smoke to communities like Washington and Greenville.

In Wilson County, dense smoke was reported near Black Creek. County officials said residents can expect visibility and breathing problems for the next few days.

The state Division of Air Quality issued a Code Orange alert for the Triangle area and Fayetteville on Thursday, saying smoke from the fire could begin to degrade the air quality in those areas. Officials said the smoky air could last a couple of days.

More than $1 million has been spent battling the fire, and close to 350 fire crews from state and local agencies, including Harnett County, were working the containment lines Wednesday. A Wake County Emergency Medical Services team was sent to the area to assist local dispatchers handling 911 calls related to the fire.