China’s northern port city of Tianjin is likely to see official gross domestic product drop by almost 20 percent in 2017 after authorities recognised severe double-counting in the port’s showcase financial district.

The revision comes on the heels of a similar acknowledgement by Inner Mongolia that implies its GDP was also inflated by about 20 percent in 2016. The magnitude of falsified data in Northern China is only slowly becoming apparent after a four-year downturn in the coal, steel and oil on which the region depends was papered over by governments eager to show robust growth.

The Binhai district in Tianjin acknowledged that it was including in its GDP the activity of thousands of companies that registered in the district in order to enjoy tax breaks, a looser forex regime or other incentives. Those firms’ actual commercial activity took place elsewhere in China.