A report of an active shooter briefly shut down a US Air Force base on Thursday in the state of Ohio, before police gave the all-clear signal in what was potentially a false alarm.
The Wright-Patterson Air Force Base said the report of an active shooter came at 12:40 pm (1640 GMT). The all-clear signal for most of the base was sent out less than two hours later, a base spokeswoman told AFP.
Emergency personnel "responded to a reported active shooter incident at the base hospital," spokeswoman Laura McGowan said.
There were unconfirmed reports that the incident could have been part of a drill that was mistaken as a real attack, according to local media.
Eyewitness Elena Arrasmith, a member of the US military who works on the base, told WHIO television that there was a planned training exercise there.
"We were just aware that it was going on," she said. "The whole base is included in the training exercise."
Television images showed people exiting the zone and its gates opened to car traffic.
Wright-Patterson is a key base for the US Air Force and headquarters to its Materiel Command, where new technologies are developed.