China's second Great Wall, a vast seawall spanning more than half of mainland coastline, may result in ecological disasters that can extend beyond the country, a new study has warned.

The seawall is a foundation for financial gain - and also a dyke holding a swelling rush of ecological woes, researchers said.

A group of scholars, including Jianguo Liu, director of Michigan State University's Centre for Systems Integration and Sustainability, outline the sweeping downsides of one of China's efforts to fuel its booming economy, that extend beyond China.

China's coastal regions are only 13% of the country's land area, but contribute 60% of its gross domestic product, researchers said. With that come layers of incentives to turn lush wetlands into engines of development and industry.

Yet the scientists outline vast ecological costs that do not appear instantly on balance sheets. They note that the wetland ecosystems support a daunting number of birds, millions of which rely on the coastlines as they migrate. The coastlines produce 28 million tonnes of fishery products, nearly 20% of the world's total.

Looking deeper reveals abundant biodiversity and a support system that also provides other invaluable but under-appreciated services for people, researchers said. For example, coastal wetlands absorb pollutants and carbon and protect people from extreme weather.

"These coastal areas are a perfect example of coupled human and natural systems. They are also a telling example of how telecoupled our world is," said Liu. "The decisions being made in China are having enormous consequences to people and ecosystem services in China and the rest of the world. We must bring ecosystem services to the business table for a sustainable future," Liu added.

The study was published in Science magazine.