If in the unlikely event of Taiwan firing cruise missiles towards Beijing, they have to choose one or more of the 3 likely flight paths,
1) fly into Fujian, Shangxi etc then all the way inland - unlikely to be successful since air defence in Fujian would have detected and shoot down incoming missiles.
2) fly along the mainland's coast line towards Shandong peninsular then turn inland towards Beijing - also unlikely to be successful due the the flight path can easily be detected by coastal air defence and navy ships (from the East Sea Fleet and North Sea Fleet) stationed along the long coastline from Fujian to Shandong.
3) fly towards Japan then turn west via Yellow Sea - Japan may activate air defence alarm if they are not informed in advance, also the South Koreans may be alerted by unknown incoming missiles. Their actions would in turn alert air defence on the mainland. Even if Japan and South Korea were informed in advance and take no action, the air defence in Dalian, Tianjin and Shandong peninsular area, and the navy ships of NSF will provide the first and second line of defence, any missiles got thro will be dealt with by the air defence surrounding Beijing. There could be some damage but this would be kept to minimum by at least 3 layers of air defence. The first layer would be air defence destroyers (051B, 052C) stationed 300 to 1000 KM from shore.
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edit delete -double posting.