A switchboard operator at the base confirmed to Reuters that a lockdown was in effect, but gave no details. A spokesman at the base said he could not immediately confirm that there had been a shooting.
According to the Fox News account, which cited an unnamed base spokesman, it was not immediately known if there were any casualties.
Trotman said the shooter or shooters had not been apprehended to her knowledge. She had no further details on the incident.
Fort Knox, near Louisville, is home to more than 40,000 U.S. military personnel, family members and civilian employees.
In February, local media reported that a soldier and his wife died of gunshot wounds at their home on the base in what the Army said appeared to be the result of a domestic dispute.