A US Air Force base was given the all-clear Friday, facility officials said, lifting a four-hour lockdown following reports of an active shooter. The Ohio base shut down at roughly 9:25 pm (0125 GMT Friday) with security forces sweeping the three-storey National Air and Space Intelligence Center.

Installation Commander Colonel Patrick Miller told local media WHIOTV that two people reported hearing a single gunshot in the Wright-Patterson Air Force Base, prompting the search.

"At the end of the night, we did not find a threat," Miller said. 

The base's official account tweeted shortly before 2 am that they had been "given the All Clear. Lockdown has been lifted".

Miller added roughly 100 people barricaded themselves in rooms during the incident.

The facility's loudspeakers -- which had been blaring for several hours so loudly it could be heard outside the base -- broadcast the all-clear, according to WHIOTV.