The South Korea connection would require rail lines through North Korea.
The undersea tunnel plan was earlier reviewed by some South Korean organizations, but the plan has not been implemented due to exorbitant construction costs worth up to 100 trillion won ($88 billion).
The tunnel will link Incheon and Weihai of Shandong Province, about 340 kilometers apart. It is not clear whether the subject of the review would be for container ships or undersea tunnels.
The Bohai undersea tunnel is 125 kilometers long, which connects Penglai, Shandong Province, and Lushun, Liaoning Province. Crossing the tunnel at 250 kilometers per hour takes 40 minutes. The construction is estimated to cost 200 billion yuan.
In August 2014, it was reported that work is likely to commence during the 13th Five-year plan (2016-2020) and construction would take ten years to complete. The current discussion is for the Bohai tunnel to be completed in 2026.
The British-French Channel Tunnel is 31.4 miles long, making it the 11th longest tunnel in use (the longest is the Delaware Aqueduct, at 85.1 miles), and the fourth longest used by rail passengers. It has the longest undersea portion of any tunnel in the world (23.5 miles.