High Power Audible Warning system

We are a large manufacturer of Urea Fertilizer.We need a warning system consisting of four to five sirens that can be controlled from two remote locations to generate six different types of tones.
Please note that we donot require lage number of small sirens but very few heavy duty sirens to cover a diameter of 3 kilometer. Average noise level at our plant is approx. 70dB and the maximum noise level is 103dB.