Plagiarism in journals I'm looking for some advice. In the course of my research on a particular area, I came across 2 papers on the same subject. One was written in 2010;  the other in 2015. Both are published in equally reputable journals, but on different continents. The three authors are all from the same continent, but not same country.

The 2015 paper is larger, and more expansive on the subject, when compared against the 2010 paper. However it has major failings in terms of bibliography (basically non-existant). After reading through both papers a number of times, to get a feel for them, I started to notice something. The 2015 paper has lifted entire tracts from The earlier paper, including citations that are not in their bibliography. The lifted pieces are not mentioned as direct quotes, and the original author is not mentioned in the bibliography.

This seems like a prima fascia and case of academic plagiarism? Any advice on what, if anything, I should do?
An interesting one, although I wouldn't jump straight to plagiarism. 

Sometimes, if the authors are all in the same research group/university/project (this could easily be across countries) they'll use bits of colleagues work with less rigorous citing than they would normally. This is especially the case if the first paper was mostly just a positioning or introductory piece.

It's not a great thing to do, but I've seen it happen on a number of occasions. However, I'd definitely get in contact with the journal of the second paper, and then if you don't hear anything constructive back then get in contact with the journal of the first paper. Definitely don't contact the authors directly unless you don't hear anything from either journal - if that's the case, get in contact with the authors of the first paper.