Liu Zhongliang, a professor involved in the research, said the tunnel is expected to bring profits of 20 billion yuan a year and boost tourism in surrounding regions.

"The project can pay for itself within 12 years," Wang Mengshu said.

Besides the profits, the tunnel can reduce the huge oil consumption required every day for cars traveling back and forth on highways, he said.

He added the Bohai Sea tunnel is a critical part of the country's 5,700-km railway project to link the cities of Tongshan in Heilongjiang province and Sanya in Hainan province.

While building underwater tunnels is not new for Chinese engineers, tunnel expert Wang still emphasized that the safety of the project will be the top concern.

"The draft plan has two chapters discussing the potential dangers in the project and the emergency plan," he said.

Tan Guangzhong, Wang's colleague, said flooding is the biggest safety risk during tunnel construction.

In the construction of the Seikan Tunnel, a slew of leaks led to financial losses and killed four workers.

Wang said the Bohai tunnel will be built at least 30 meters below the seabed, which is mostly hard rock.

Besides unforeseen accidents, complicated geologic structures may pose challenges in the construction, especially when two major fault zones are in the region.

The Tanlu and Zhangjiakou Penglai fault zones have been sources of chronic seismic activity. The Tangshan earthquake in 1976 killed tens of thousands of people.

Matthias Loftsson, director of geology for Iceland's Mann-vit, which has decades of experience in land and sub-sea tunnel design, engineering and consulting, highlighted safety concerns.

"In general, though, one can say tunnels are not unsafe in earthquake areas, all depending on the geology, tunnel depth and other local conditions," he said.

"However, excavation of a tunnel through active faults, where displacement can occur with a potential danger of flooding, would be of great concern and needs special attention," Loftsson said.

Liu Jie, director of the China Earthquake Networks Center, agreed that Northeast China is unstable, with earthquakes of less than magnitude-5 frequently occurring, especially after a massive magnitude-9 earthquake in Japan in 1999 caused large-scale movement of the lithosphere, or the Earth's rigid surface.

Zhang Chunyan in London contributed to this story.