Reviewing a journal paper

I'm currently reviewing a journal paper that's interesting but the presentation is very poor. It's badly organised and the misuse of notations is terrible.

The paper is 30 pages long and I've gone through the first 10 pages (I have 4 pages of comments so far) and I'm getting more and more annoyed at the presentation and the authors sloppiness. I know I signed up to referee the paper but on the other hand I feel that I'm not the one that should clean up the paper. The authors should see to it that it's in good shape when they submit it (I know I'm throwing rocks inside a glass house...).

Can I send back a review report of the first 10 pages urging the authors to improve the writing before they resubmit or do I have to continue to review the remaining 20 pages?

This reminds me of my master thesis (30 pages) that I submitted to a journal about ten years ago. I got back two referee reports three years later containing comments up to page 15 together with the rejection letter. I remember I was terribly disappointed :-)