More than 30,000 government employees, civilians and contractors work daily at Redstone.
All of Redstone's perimeter gates have been closed, and staff members have been told to shelter in place, Hanson said.
The Sparkman complex and intersections in and around Martin Road remained in a lockdown, officials said. The massive installation hosts several military and civilian organizations, including the Army Aviation and Missile Command and NASA's Marshall Space Flight Center.
According to a tweet from the base, there is a possible active shooter on the arsenal.
The base's statement about the training exercise planned for this week read: 'AMCOM will be conducting an Active Shooter exercise at Redstone Arsenal (USAG-R) during the week of 25 June.
"First reports are quite often wrong", Christopher Colster noted during an interview with WAFF.
The Arsenal's Twitter account posted that the "installation is locked down".
NASA's Marshall Space Flight Center issued an alert about an "emergency situation" near the Sparkman Center, the headquarters for the Army's Aviation and Missile Command at Redstone.
The congressman for Alabama's Fifth District, Mo Brooks, said he was monitoring the situation.
"I will continue to closely monitor and pray for a peaceful and quick resolution", Ivey said on Twitter. "And also this would include Redstone Arsenal who has also been associated with this case".
Originally a chemical weapons manufacturing facility for World War II, in the immediate post-war era it became home to the German rocket scientists that were brought to the U.S. as part of Operation Paperclip. The German design team was then spun off to become part of the newly foundedNASA.