Wright-Patterson Air Force Base was placed on lockdown for over four hours Thursday evening into early Friday morning.The base’s command center operator confirmed that the base was placed on lockdown at around 9:35 p.m. The lockdown was announced over loudspeakers.According to the 88th Air Base Wing, authorities responded to a report of an active shooter in the National Air and Space Intelligence Center in Area A at Wright-Patterson Air Force Base. Two people believed they heard gunshots and reported it, which led to a response.Officials said security forces are currently sweeping the building while the base is on lockdown. It's unclear at this time if shots have been fired which is why security is sweeping the building.The three-story building is about 850,000 square feet. Officials said there's a lot of secure spaces, some of which are owned by other agencies. People are having to come in to provide access to secure spaces so that security forces can complete their sweep.Therefore, the size of the building and the search of secure spaces is why the search took several hours to conduct and continued into the overnight hours.The lockdown means no one was allowed to come in the building, leave the building or move about on base. Employees and residents were to stay in their building or house and only key emergency officials were allowed to move. Local law enforcement were staged for mutual aid if needed.At around 1:45 a.m., officials announced an "all clear" at Wright-Patterson Air Force Base and lifted the lockdown. They did not report their findings but said they would release more information when available.No injuries have been reported at this time."We understand there are concerns and questions," 88th Air Base Wing tweeted just before 11 p.m. "Our first priority is to protect our people. All of our military and civilian employees are trained to quickly assess the situation and take appropriate action."Nearby, Wright State University sent out a message to students and employees saying they should stay clear of the areas toward the north end of campus, such as Kauffman Avenue and Ohio State Route 844. Students are advised to "take appropriate safety precautions to protect themselves if necessary."Wright-Patterson Air Force Base is located just east of Dayton, Ohio.WLWT has a reporter at the scene and will provide updates when more information is available.