A US army base is in lockdown due to reports of a “possible active shooter” on the loose with troops being told to “run, hide and fight”.

All gates to the army base in Madison County, Alabama, have been closed amid reports of an “emergency situation” possibly involving an gunman.   Redstone Arsenal tweeted out to confirm reports of a possible active shooter.

An email sent to employees at 10.31am local time said: “This is a real world event, which is not part of the exercise. The facility is under lockdown and all gates are closed. More to follow. This is NOT AN EXERCISE.”