Seeing how PRC is always voicing its concern on a US and Japanese aggression, what type of defenses are set up on the eastern coast of the country to deter a attack? Are there any key fortifications?
The JMSDF lacks offensive weapons (LGBs, LACMs, long-range bombers) and is not a "threat" to the PRC mainland per se. But in conflicts over ocean territory, the Japanese navy out-class the PLAN in technology, training, and experience. To cite just one example, I think the Japanese are better at ASW.
The PLAN and PLANAF has staretd addressing some of their short-comings by obtaining Su-30's, JH-7's, and some modern DDG's and FFG's. But it'd be some years before they can match the Japanese toe-to-toe. The USN is far larger than the Japanese navy, and I don't foresee the PLAN to match the USN within our generation, unless something drastic happens that cause the downfall of US government. The PLAN could, however, provide some degree of deterrance via submarines in the littoral region.
I think for the most part, we've evolved beyond the traditional fortified strongholds, except deep underground bunkers. Fixed defenses are basically stationary targets for whoever that wins air superiority. The closest I think of that resembles "strong point defense" for the PLA would be the numerous mobile SAM sites along Taiwan's coast and rings around important cities (Beijing). I think when China first imported the S-300's, they put them around Beijing.
p.s. by "defense" I think we'd exclude offensive weapons like the numerous SRBM's and MRBM's that the PLA has deployed the the area.