The base, which is home to Air Force One and thousands of military personnel, was briefly sent into confusion. Law enforcement streamed across the facility, cable news carried live updates on the incident, and a trip from the base by Vice President Biden was delayed.

The person reported the active shooter situation at about 9 a.m., after misidentifying security forces who were conducting a routine inspection of the Malcolm Grow medical facility as a potential threat, the officials said. Officials would not say whether the security team was armed.

The base sent out an order to shelter in place a short time later. Authorities could be seen moving across the campus in black SUVs and later evacuating people from the medical facility. One person who works at the base said he received an email warning that told employees to remain locked in their offices and read: "This is a real-world event. Active shooter."