China's mission to bulldoze mountains in order to create land to build on could cause environmental problems, according to researchers.
Researchers from Chang'an University in China have issued warnings that dozens of mountains have already been flattened, which has caused water and air pollution, flooding and soil erosion.
The researchers said that this activity is happening on an unprecedented scale.
"Because there have been no land creation projects like this before in the world, there are no guidelines," said Professor Peiyue Li, from Chang'an University's School of Environmental Science and Engineering, according to BBC News.
Since China's cities are rapidly expanding as its economy grows, moving mountains is one way to supply more land for development.
Approximately one-fifth of the country's population lives in mountainous areas, according to BBC News.
In cities like Chongqing, Shiyan, Yichang, Lanzhou and Yan'an, dozens of hilltops have already been levelled.
"Mountainous cities such as Yan'an are mostly located in relatively flat valleys," said Li. "The valleys are narrow and limit the development of the cities - and huge population density is also a factor."
Though mountaintop removal is occasionally used by the mining industry, especially in the U.S., researchers believe the scale of this in China is "unparalleled," according to BBC News.
The researchers have warned that turning hills into plains is throwing dust particles into the atmosphere, causing landslides, polluting waterways, flooding and endangering plants and animals.
They also believe that the flattened land could also be unsuitable to build on.
"The most concerning issue is the safety of constructing cities on the newly created land," said Li. "Yan'an, for example, is the largest project ever attempted on land that is composed of thick windblown silt. Such soft soils can subside when wet, causing structural collapse and land subsidence. Building on such soils is quite dangerous and it would take a very long time for the ground base to become stable."
The scientists believe the Chinese government should work with international and national experts to access the risks before they continue, according to BBC News.
Their study appears in a recent edition of the journal Nature.
"In the US and China, we're moving ahead without much insight into what the result will be, especially when it comes to the water, the hydrology, the water quality implications," said Prof Brian McGlynn, from Duke University, according to BBC News. "The (comment) article focuses on the structural issues, the ability of the land to stabilise. In addition to that we're massively changing the flow of water and material it comes into contact with.