The field and woods fire broke out before 2 p.m. in the 1200 block of Macton Road, according to the Harford County Volunteer Fire & EMS Association.
After 3 p.m., Harford County Emergency Management reported that Macton Road, Prospect Road, Mill Green Road and Davis Corner Road were closed near the blaze.
Traffic was being rerouted in the area, and Harford County Public Schools was rerouting students from the north Harford area as a result of the fire activity and road closures, according to emergency management.
Harford Fire & EMS spokesman Rich Gardiner reported before 3 p.m. that the fire was not under control.
Located in the 1200 block of Macton Road, the blaze was exacerbated by wind and primed fuels, Gardiner said.
The National Weather Service issued an alert due to an enhanced threat of wildfires through Thursday evening as the result of low humidity, gusty winds and low fuel moisture.
The greatest threat is accidental debris burning, according to the weather service.
Nobody was injured in the fire off Macton Road, which drew first responders from Harford and York counties, Harford Fire & EMS reported.
Darlington, Jarrettsville, Norrisville, Level, Aberdeen, Bel Air, Whiteford, Havre de Grace and York County responded, according to Norrisville.