The Pingtan Comprehensive Pilot Zone has invested about 5 billion yuan ($8.2 billion) in the construction of its underground infrastructure.

The local government calls the initiative an "invisible" civic project, and it concerns an integrated underground pipeline ditch that stretches 120 kilometers in the urban area of Pingtan.

The ditch – which contains gas pipes, electric cables and water pipes - is large enough for specialists to do maintenance work.

Workers took two years to complete the 3.5-kilometer section under Tanxi Boulevard, one of the busiest streets in Pingtan, and they put the finishing touches in September. It now contains a high-voltage cable and water pipes, and the 8.25-meter wide, 4-meter-high space can also hold vehicles.

Shang Wuxiao, head of the construction team responsible for the project, said that the integrated pipeline ditch is one of the largest engineering projects in Pingtan that aims to improve the lives of the local population, and only a few Chinese cities have completed such a project.

Liu Donggang, a manager of a local company specializing in traffic investment, said that the cost of the ditch amounts to more than 70 million yuan per kilometer, which is high but could no doubt help reduce the county's overall expenditure.

He also said that the ditch could perhaps help save almost 533 hectares of land, and that the fact that various pipes are located in a single ditch keeps the city tidier, and it is also easier to carry out maintenance work. In addition, Liu said that this method also makes efficient use of underground space and enhances the county's comprehensive capabilities of disaster prevention.

The power company was the first local enterprise to use the integrated ditch and, in late July, a 220-kv electric line began running through the ditch to reach a transformer substation in Zhuyu village.

"Without the ditch, we would have had to erect electrical transmission towers, which would definitely take up enormous land. The ditch also makes maintenance more convenient and cable safer," said Liu Huadong, an employee of the Zhuyu transformer substation.

Edited by Chen Zhilin and Niva Whyman