Beijing included a cross-strait high-speed rail network in its then-new five-year plan. But a lot of work has been need to get a viable technical design.
There is also the political challenge. Taiwan does not want the tunnel and a majority do not want reunification with China.
The China-Taiwan tunnel would start from Pingtan, a pilot free-trade zone area set up by Beijing in Fujian province in 2013 to boost trade with Taiwan. Digging would go down nearly 200 meters (218 yards). It would cut through complex layers of rock, including extremely hard granite and avoid at least two major earthquake faults and return to the surface in Hsinchu, a coastal city near Taipei.