Air quality across much of eastern North Carolina has reached unhealthy levels in several coastal counties as a 55-square-mile wildfire burns the Croatan National Forest, the state Department of Environmental Quality said Saturday.

Twenty-one counties have been under alerts for air quality. The department's Division of Air Quality warned that the Great Lake wildfire in southwestern Craven County has blanketed coastal North Carolina and parts of Virginia in heavy smoke and falling ash.

The fire was first detected Wednesday evening and spready rapidly Thursday due to dry and windy conditions, according to the U.S. Forest Service. Craven County officials said the fire was about 10% contained as of Saturday.

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Air quality across many parts of North Carolina has reached unhealthy levels due to a wildfire in the Croatan National Forest.

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Craven and Jones counties, which are directly downwind from the fire, are under a Code Purple alert — meaning the air quality is "very unhealthy" — due to particle pollution. Anyone who can see or smell smoke is advised to stay indoors.

In counties further downwind, the Division of Air Quality warns some people may experience health problems from prolonged exposure to polluted air. Children and residents with respiratory conditions, like asthma, are advised to avoid outdoor exercise.

The air quality alerts will remain in effect until midnight Saturday. State air quality officials say a passing cold front late Saturday may push the smoke to the east.