Unconfirmed reports suggest the man has barricaded himself in the hospital.
A spokesperson for the base in Drayton confirmed on Twitter that emergency services were on the scene, with the base’s 27,000 employees told to take shelter.
It tweeted: “At approximately 12:40pm today, base emergency responders, including security forces and fire department, responded to an incident in building 830, the Wright-Patt Hospital.
“Base personnel have been directed to shelter in place until the incident is investigated.
“Our first priority in any emergency incident is to protect the men and women at Wright-Patt.”
At around 2:40pm local time, the Wright-Patterson Air Force Base gave the all-clear to base personnel, advising the threat has passed.
People are still being asked to avoid the area around the hospital.
“Our base security forces defenders and fire department personnel are trained to quickly assess situations and take necessary action.”
Wright State University and nearby schools had gone into lockdown after the first alerts of the incident went out.
Around 20 minutes later, the university tweeted that they had been told that the incident had been “contained
Elena Arrasmith, who works as an administrator at the base, told WHIO TV that she was on a break from training exercises and discovered the base in lockdown when she returned.
She said: “We were just in our exercise,” Arrasmith said. “I left for lunch and came back to a real world event happening.
“I do know that there was an active shooter real world event.”
Ohio Senator Sherrod Brown had issued a statement on Twitter, asking for prayers from the community.
He wrote: “People join us in keeping the first responders, Wright-Patt personnel and the entire Dayton community in our thoughts as we pray for the safety of everyone involved.”
The Wright-Patterson Air Force Base was built in November 1917 and in 1995, negotiations to end the Bosnian War were held there, resulting in the Dayton Agreement ending the conflict.
The military base, near Dayon is southwest Ohio, was scheduled to host quarterly base-wide exercises from July 30 until August 3.
This is a breaking story. More to follow.