unzip

In case normal unzip can't handle them properly (I was unable to make it do it properly) use 7 zip instead (package p7zip) - command to use is
7z x path_to_zip

It can be done with port installed, but first multivolume zip has to be converted to single volume zip file.

First run
zip -FF path-to-multivolume-zip --out path-to-singlezip
to convert to single volume, then you can unzip that one as usual.