Similar news detection How do top news portals detect similar news? For example https://www.bbc.com/news/world-asia-china-51431087, if you go to this webpage, you can see the "More on this story" section at the bottom of the page. This news was published today, but it has detected similar news from days ago. 

Is there any known algorithm or any library?
This is a proprietary system so we have no way of knowing.

In general, you will find a lot of work and potential solutions by searching for text similarity or document similarity. For starters, you could have a look at the work of Islam and Inkpen [1] on short sentence similarity (it mentions plenty of other references you can widen your search to) or a more general survey of Gomaa and Fahmy [2].

If you are interested in libraries, NLTK might be helpful.



[1] Islam, Aminul, and Diana Inkpen. "Semantic text similarity using corpus-based word similarity and string similarity." ACM Transactions on Knowledge Discovery from Data (TKDD) 2.2 (2008): 1-25.

[2] Gomaa, Wael H., and Aly A. Fahmy. "A survey of text similarity approaches." International Journal of Computer Applications 68.13 (2013): 13-18.