The counties that form the Xiongan New Area in Hebei province have shut down thousands of polluting companies since the move to create the area was announced in April.

More than 7,200 companies that discharged heavy pollution were investigated and nearly 4,000 were closed, according to an announcement on the area's public WeChat account.

About 100 people involved were arrested and detained for questioning about contaminating the environment.

The severity of the punishment showed the determination of the area's leaders to tackle environmental problems, observers said.

Officials in the Xiongan New Area, a zone established to advance the coordinated development of the Beijing-Tianjin-Hebei region, have been ordered to always put the environment first and to adhere to green development.

When plans for the area were unveiled four months ago, one of the declared goals was to create a "naturally scenic city with blue skies, fresh air and clean water".

Located about 100 kilometers southwest of downtown Beijing, Xiongan spans Xiongxian, Rongcheng and Anxin counties in Hebei province.

It also covers Baiyangdian Lake, a major wetland that covers 366 square kilo-meters and is believed to be a key in improving the area's overall environment.

But Baoding, in the new area, usually is one of the 10 cities with the country's worst air quality. Also, Baiyangdian's ecology has been damaged by years of pollution from fish-raising and industrial discharges.

To control the pollution, the three counties have taken a series of measures.

Anxin, which covers most of the lake, is focusing on eliminating fish net cages, which pollute the water with fish feces and leftover bait and have been in use for years.

The county also ordered all illegal gas stations to be closed and demolished.

Rongcheng has barred villages near Baiyangdian from raising livestock, which would endanger the lake's water quality.

"All livestock farms must be closed by the end of October," the county's government said in a statement.

The county also recently started a crackdown on factories - mainly garment factories, dyeing plants and paper mills - that illegally dispose of wastewater.

Xiongxian will close all plastics factories, printing and platemaking plants, and any factory that discharges wastewater illegally.