Updated at 2:20 p.m.: All floors of the building have been reopened.
Fire officials have reopened the Loudoun County Government Center after odor, haze, and apparent electrical smoke on the second floor prompted a fire alarm and evacuation. One person was transported to the hospital for treatment.
Harrison Street between Market and Loudoun streets has also been reopened after closing during the event.
The smoke is believed to have come from the HVAC system.
Approximately 500 people work in the building.