Update: Gov. Kay Ivey said Alabama Law Enforcement Agency assisted with operations at Redstone. The governor said there was no shooter.
Redstone Arsenal was completely locked down for about two hours on Tuesday amid reports of a possible active shooter near the Army's Aviation and Missile Command headquarters.
Workers were told to "run hide fight" before the lock down was lifted around 12:30 p.m. The incident occurred in the Sparkman Center, which remained locked down Tuesday afternoon.
Redstone officials haven't confirmed what triggered the active shooter notice. Garrison spokesman Christopher Colster said he hasn't received any details about the incident, which remains under investigation. Colster said he could not confirm whether anyone was shot or otherwise injured. It wasn't clear whether any suspects were identified or anyone was taken into custody.
The area surrounding the Sparkman Center remains "restricted" this afternoon even though the lockdown was lifted and gates reopened. Detours remain possible until 3:15 p.m. near the Sparkman Center.
"We do not believe there is a threat or we would not have opened the installation back up," Colster said.
Police vehicles blocked the entrance to Arsenal gates earlier today. Images on social media showed an ambulance and what appeared to be civilians standing outside the Sparkman Center, which includes multiple buildings with offices, an auditorium, cafeteria and an interior courtyard.
Amy Jay, whose husband was working at the Sparkman Center, told The Associated Press he learned the situation was over through an announcement over the building's public address system.
"Feeling like I can breathe again!" Jay wrote in a message to The Associated Press. "My husband is a contractor and a veteran so when we hear things like this we're reminded of what happened at Fort Hood," she said, referring to the 2009 shooting at a military base in Texas.
This week was designated for active shooter training at Redstone, specifically with a drill scheduled for Wednesday. Because officials had announced the training ahead of time, there initially was some confusion about whether a reported "emergency situation" was just a drill.
Before 10:30 a.m., Redstone issued Tweets to confirm the situation was not a drill.
Officials haven't said whether training exercises will happen Wednesday.
More than 30,000 government employees, civilians and contractors work daily at Redstone. It is home to Army missile defense programs and other military offices.
NASA's Marshall Space Flight Center, which oversees rocket propulsion operations, also is located at Redstone.