There are also Current sensors with integrated amplifiers to 1KA mfd by Lem Electronics. I have 15 300 A hall effect devices that would be perfect for your application.
Part #: Hal 300 S. The thing that makes them "better" than the Allergro devices mentioned is that you don't have to physically connect to the circuit being measured. You simply pass a wire through the hole in the device (20 X 15 mm - .6 X .8"). Both are hall effect transducers but the Allegro requires a special type of PCB to connect the device to the circuit to be measured, one that can handle the full current being measured. I've attached a data sheet for both.
Doc
hal standard_e.pdf (480 KB)
ACS756-Datasheet.pdf (352 KB)