China is planning to build the world's longest underwater tunnel at a whopping cost of 220 billion yuan ($36 billion).

According to state-run China Daily, the government will begin to undertake a feasibility study as early as 2015.

The underwater tunnel will help reduce travel time between two northern port cities Dalian to Yantai. The tunnel's blueprint will be submitted in April before the State Council, China's Cabinet.

"Once approved, work could begin as early as 2015 or 2016," Wang Mengshu, a tunnel and railway expert at the Chinese Academy of Engineering who has worked on the plan since 2012, told China Daily.

"The underwater tunnel is expected to be completed within the period of the 13th five-year plan (2016 to 2020)," said Wang.

With a planned lifespan of 100 years, the proposed 123-km underwater tunnel will house a rail line connecting the port cities of Dalian in Liaoning province and Yantai in Shandong province. It will follow the coastline to the west of Yantai before going north across the Bohai Sea.

"Using the tunnel, it will take only 40 minutes to travel from Dalian to Yantai," Wang said.

At present, traveling to Dalian to Yantai and vice versa consumes eight hours by ferry. Once operational, travel time will be slashed to 40 minutes between the two port cities.

Trains passing through the Bohai tunnel will run at 220 kilometers an hour, the China Daily reported. Passenger vehicles meantime will pass through the tunnel on rail carriages.

This is not the first time China announced the presence of such an ambitious project. As early as 1994 the country had wanted to build it at a cost of $10 billion. Its completion was set for 2010.

Japan operates the world's longest undersea tunnel, the Seikan. Launched in 1988 after more than two decades of construction, Seikan is 31 miles long.