Render React Components in Twig Templates
After doing some research, I found 3 options to render React components on the server side. 


Use the PHP V8Js extension to run an embedded V8 engine
Execute node.js processes on demand
Run a node.js rendering daemon for rendering


Rendering on the server side is beneficial for performance of the initial page load. Using the V8Js extension and a twig extension like Tesonet seems like the best option for me. 

V8Js installation instructions can be found here

Some other good options to try out are: React Renderer or symfony-react-sandbox or React Bundle. Symfony React Sandbox integrates React Bundle. React Bundle integrates React Renderer. 

Read more here