Random endo-hydrolysis of N-acetyl-beta-D-glucosaminide (1->4)-beta-linkages in chitin and chitodextrins. Stimulated by magnesium ions; inhibited by N-bromosuccinimide and 2-hydroxy-5-nitrobenzyl bromide. Optimum pH is 8.0. Optimum temperature is 50 degrees Celsius. Belongs to the glycosyl hydrolase 18 family. Chitinase class II subfamily.