A red dust that emanates from a Chinese-owned steel mill in Serbia’s Smedrevo city has led to a four-fold surge in cancer cases in region and local residents want the plant to shut down, according to a Reuters news report.

According to data from the Smederevo public health body, which a watchdog called Tvrdjava obtained through a freedom of information request and shared with Reuters, the municipality of around 100,000 people reported 6,866 cancer cases in 2019, up from 1,738 in 2011.

The city of Smederevo is located in central Serbia, on the right bank of the Danube river, only 45 kilometers downstream of the capital Belgrade.

The Reuters report cited a local resident who was suffering from throat cancer as saying that they have to dry their laundry indoors and use vinegar to clean the red dust from their cars as water cannot wash it off.

The plant says it has invested 300 million euros in technology and pollution reduction since China's biggest steelmaker, Hesteel bought it from the Serbian state for $53 million five years ago.

While the plant manager denies its pollution is causing cancer, activists say the plant is an example of Chinese-owned industrial firms ignoring pollution standards.

Nikola Krstic, the head of Tvrdjava, an environmental group whose name means The Fort, said an analysis of the red dust in September showed high concentration of heavy metals.

"The air in the town is far below European standards for 120 days per year," he told Reuters. "Red dust is greasy, it sticks to lungs, makes breathing difficult."

China has invested heavily in Serbia, a country which has differences with the West and enjoys a close relationship with Beijing.

In April, Serbia's authorities ordered China's Zijin Mining Group to temporarily halt some operations at the country's only copper mine over failure to comply with environmental standards. The mine said it would rectify all the problems swiftly, and it was permitted to reopen.