Redstone Arsenal officials found no evidence of an active shooter today on the Huntsville military base following a two-hour lockdown and investigation.

The Arsenal was locked down Tuesday morning after two calls were made to 911 about a possible active shooter at the Sparkman Center, the Army's Aviation and Missile Command headquarters. The callers reported hearing shots fired, with one saying a weapon was seen.

Col. Tom Holliday, Garrison Commander at Redstone Arsenal, said there was no active shooter. The Sparkman complex was given the all clear just before 3 p.m.

"What I really want to make clear when it comes to the safety of our work force, our systems worked," Holliday said. "That was proven today."

Holliday said there were medical calls associated with people who were evacuated from the building, in part due to the heat. No other injuries were reported, he said.

The Army's Criminal Investigation Division is probing the matter.

Gov. Kay Ivey said the Alabama Law Enforcement Agency assisted with operations at Redstone. The governor also confirmed there was no active shooter.

Arsenal workers were told to "run hide fight" before the lock down was lifted around 12:30 p.m.

Holliday told reporters he does not believe officials overreacted to the 911 calls. But, "I'd rather overreact than underreact," he said.

Huntsville Mayor Tommy Battle praised the response of local, state and federal law enforcement. He called the incident a "potential problem that could've been life threatening."

"This is one day that thoughts and prayers were answered and thank goodness for that," Battle said. "Thus far we've found no event that would cause us to have concern, so that's a great thing for Huntsville and it's a great thing for Redstone Arsenal. It's kind of fitting that this is Armed Forces Week and this shows our partnership with Redstone Arsenal. When this event happened, our police were out there working with their security guards and their security and we were able to make sure that nothing happened."

Holliday noted the Sparkman Center is 1.5 million square feet. That, he said, is part of the reason why it took several hours to clear the building and determine there was not an active shooter.

Officials are investigating whether the reports of a possible active shooter were part of a hoax, Holliday said. Investigators also are probing whether the reports were made because of active shooter drills that were previously scheduled to happen on the Arsenal this week. The drill, scheduled for Wednesday, has been cancelled.

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.

"We do not believe there is a threat or we would not have opened the installation back up," Redstone spokesman Chris Colster said after the lockdown was lifted earlier today.

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.

Redstone is home to Army Aviation and Missile Command, Army Materiel Command, Marshall Space Flight Center, Redstone Arsenal, ATF and FBI facilities.

My office is being updated about the situation @TeamREDSTONE I will continue to closely monitor and pray for a peaceful and quick resolution — Governor Kay Ivey (@GovernorKayIvey) June 27, 2017

Redstone is home to Army Aviation and Missile Command, Army Materiel Command, Marshall Space Flight Center, Redstone Arsenal, ATF and FBI facilities.

Possible active shooter on the Arsenal. Installation is locked down. Run hide fight. — Redstone Arsenal (@TeamRedstone) June 27, 2017

Possible active shooter on the Arsenal. Installation is locked down. Run hide fight. — Redstone Arsenal (@TeamRedstone) June 27, 2017

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