TAIYUAN, Jan. 6 (Xinhua) -- In the city of Jiexiu, northern China's Shanxi Province, a 1,600-year-old, once dilapidated underground tunnel has been returned to its original glory.

The 10,000-meter-long tunnel was a military defense in ancient China. However, due to a dearth of proper protection, it decayed with the Zhangbi Castle, a Chinese-style architecture situated just above it.

"We have spent almost 600 million yuan (86 million U.S. dollars) to restore the cultural tunnel and the castle," said Zhang Jinxiang, with a local coal company. "We repaired the decaying old buildings and consolidated the tunnel."

In the coal-rich Shanxi Province, many have joined in efforts to protect local cultural relics through social capital, including those from the coal industry, seeking changes amid safety scrutiny and environmental woes.

So far, 88 relics have received sufficient funds for restoration in Shanxi, according to the latest government figures.

Shanxi Province has more than 900 coal mines, with an annual output of 900 million tonnes. About 300,000 coal miners in the province are working long hours underground.

China has slashed coal production in the province in recent years, with authorities having suspended or held back the construction of 82 coal mines in the first five months of 2019.

Meanwhile, in the historical province of Shanxi, more than 5,500 ancient buildings have survived the test of time. But the local government was shy of funds to protect relics and had to resort to social capital.

"Only about 3,000 cultural remains have obtained funds for protection, and the rest are still vulnerable," said Zhao Shuguang, with the Shanxi Culture Relics Bureau.

Under such circumstances, many traditional coal companies are using this opportunity to transform themselves by switching to the tourism industry.

Zhang Jinxiang, with the coal company, said they have signed an agreement with the Shanxi government, with every detail of the repairs under government supervision.

The government trusted the company to turn the Zhangbi Castle and the tunnel into a national-level tourist attraction in 2009. Today, the castle generates 10 million yuan in ticket sales revenue annually.

The company's role change also benefited many local villagers who used to depend on the coal industry for survival.

"I feel relaxed selling tourism souvenirs here," said villager Li Qijin. Li used to be a coal miner in the city. "Men and women in the village now rely on tourism," he said.

The central government is also encouraging social capital to protect relics, with a State Council guideline emphasizing the role of social capital.

However, the inflow of social capital also increases the risk of damages to cultural relics. To enhance supervision, authorities are building a digital platform where all local cultural relics will fall under their watch.

"This will allow us to prevent any relic vandalism," said Zhao Shuguang, the Shanxi culture relics official.