Two people were taken to a hospital after an incident outside the gate of the Little Rock Air Force Base in Arkansas on Monday, sending the installation into lockdown, the base said in a statement.
The Arkansas Democrat-Gazette quoted a police source as saying a person was shot while apparently trying to gain access to the base outside of Little Rock.
Base officials did not provide details on whether there had been a shooting.
Base officials said "an active threat occurred at the front gate to Little Rock AFB" at about 9:15 a.m. CDT.
All base gates have been closed to traffic.
"All personnel and visitors are advised to stay away from the main gate area until further notice," the base said in a Facebook posting.
The base is home to the 19th Airlift Wing and has more than 8,000 active-duty military and civilian members, it said on its website.