A new "Great Wall of China" is being built that will eventually see an urban sprawl along 1800 kilometres of the Yellow Sea, placing additional pressure on tidal flats now visited by shorebirds on their annual migrations between Australasia and Arctic Russia.

Other pressures in a region that includes South and North Korea range from pollution and weed invasion to the damming of rivers and construction of off-shore wind farms.

So far some two-thirds of the tidal flat ecosystems have been destroyed, with a further two per cent disappearing annually, said Nicholas Murray, a conservation biologist now with the University of NSW.

"The destruction is in the order of what you see in tropical forests," Dr Murray said. "Even in protected areas, there are illegal developments that impact the tidal flats."

Among the bird species at risk are the threatened curley, bar-tailed godwit and the great knot. Some of the birds weigh only "as much as couple of box of matches" and can double their weight in a couple of weeks at the vital feeding stops before continuing their journey, Dr Murray said.

In a paper published this month in Austral Ecology, Dr Murray and fellow researchers Richard Fuller from the University of Queensland and Ma Zhijun from Shanghai's Fudan University, used remote sensed habitat data to declare the status of the ecosystem to be endangered, according to International Union for Conservation of Nature criteria. The future is "grim", the paper concludes.

The increasing frequency of algal blooms, hypoxic dead zones and jellyfish blooms were all symptoms of an ecosystem in a decline that had to be halted immediately, Dr Murray said.

The modification of rivers such as the Yellow River and the Yangtze meant the natural replenishment of the flats had been curtailed, leaving them subject to erosion, Dr Murray said, adding that rising sea levels caused by climate change would add to the erosion pressures.