The guard came across a man at 2.20am trying to open a window on the premises.
Springs police spokesman Capt Johannes Ramphora says two more men arrived and tied the guard’s hands and legs.
They pushed him under a bakkie that was parked on the premises.
Ramphora says although nothing was stolen from the building, the robbers took off with the guard’s two cellphones.
Anyone with information, can call police on 011 365 5700/19/20.