UPDATE: The lockdown at Travis has been lifted after police found no shots fired. The updated story can be found here.
Travis Air Force Base in California on Wednesday ordered personnel to shelter in place in response to a "real world security incident."
Travis said on its Facebook page at about 3:30 p.m. Pacific time that officials were responding to the incident, and asked the public to stay away so emergency responders could deal with it. About 15 minutes later, the base said on its official Twitter feed that a shelter in place had been declared, and that people should lock doors and windows.
In response to a comment on the original Facebook post, Travis said that the warning was not connected to a base exercise already scheduled for the day.
Local TV station CBS13 in Sacramento, citing a witness at the scene, reported that there is an active shooter at the shopping center on base. Air Force officials have not verified the report.
The alert came hours after a gunman shot and wounded Louisiana Rep. Steve Scalise, a congressional aide, a lobbyist and two Capitol Police officers at a baseball practice in Alexandria, Virginia, raising tensions across the country. There was also another mass shooting at a UPS facility in San Francisco Wednesday that killed four and wounded two.
This is a breaking news incident. This story will be updated as events unfold.
Stephen Losey is the air warfare reporter for Defense News. He previously covered leadership and personnel issues at Air Force Times, and the Pentagon, special operations and air warfare at Military.com. He has traveled to the Middle East to cover U.S. Air Force operations.