(CNN)The US Army's Redstone Arsenal post in Huntsville, Alabama, is on lockdown because of a "possible active shooter," the facility's Twitter account said Tuesday.

There were reports of a shooter at Building 5301 -- the Aviation and Missile Command building -- at the post's Sparkman Center, Army spokeswoman Kim Hanson said.

"Installation is locked down. Run hide fight," the post's Twitter account said.

An Army email sent to facility personnel and relatives was more explicit, saying an active shooter was on Building 5301's second floor.

"If you are not in the Sparkman Center, stay away from the area," said the email, sent at 10:08 a.m. CT and obtained by CNN.

Possible active shooter on the Arsenal. Installation is locked down. Run hide fight.

— Redstone Arsenal (@TeamREDSTONE) June 27, 2017

All of Redstone's perimeter gates have been closed, and staff members have been told to shelter in place, Hanson said.
An ambulance service has been sent to the facility, said Kristin Clark, a dispatcher for Huntsville Emergency Medical Services.
Emergency vehicles are outside a gate Tuesday at Redstone Arsenal in Huntsville, Alabama.

The FBI said its agents are headed to the scene. Base security personnel were working with the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives, Hanson said.
Alabama Gov. Kay Ivey said her office is being updated about the situation.