"We do have some solid reports that two gunshots were fired into the installation," Lieutenant Colonel Brian Loveless told reporters at Joint Base San Antonio, Reuters reported.
The base issued an "active shooter warning" and ordered all personnel to implement lockdown procedures following the initial reports, according to a message on the facility's official Twitter account.
San Antonio Police had no comment and referred queries to Joint Base spokespersons, who could not be reached immediately.
In 2016, two airmen were killed at the base in what military officials said was a "workplace violence incident."
The joint base, formed through the consolidation of two Air Force bases and the Army's Fort Sam Houston in 2010, provides basic and advanced training to military personnel.
ZZ/PR