A larger explosion followed by gunfire was heard at a state-owned company in the aviation and defense industry, Turkish media report.
According to Ali Yerlikaya, at least three people have died and 14 have been injured.
Several Turkish media outlets report that the "terrorists" took a taxi to the site during a shift change. One of them is said to have detonated a bomb while the others entered and began shooting.
CNN Turk and other TV channels have published images from surveillance cameras showing both smoke columns and men with automatic rifles.
However, the state media council RTÜK issued a ban on publishing images and audio from the site in the late afternoon.
The state-controlled TAI, also known as Tusas, is a technical center for the design, development, and production of aircraft and aircraft platforms in Turkey. It also includes drones and parts for F-16 fighter jets.
Security forces, ambulances, and rescue services have been alerted to the site, according to NTV, which shows images of a large cloud of smoke from the Kahramankazan area, located about 4 miles from the capital.
Most of the employees at TAI have been taken to a safe area, according to reports.
