On the fifth day of China’s “smog pocolypse,’’ thousands of factories continue to operate in spite of orders to temporarily shut down during a government issued pollution “red alert’’.

It was business as usual on Wednesday in central Henan province where nearly 3,000 companies had been ordered to stop polluting, according to reports.

Another 900 companies in the province told to reduce their emissions have not done so, said Xu Ganlu, deputy governor of Henan.

Henan’s government launched a 72-hour campaign of factory inspection late Monday, vowing to penalise those who disobeyed the emergency strictures.

The education bureau in Henan’s provincial capital, Zhengzhou, ordered all primary schools to cancel classes out of health concerns.

But in pollution hotspot Shijiazhuang, kindergartens, primary and middle schools stayed open, local media reported.

One staff member of a Shijiazhuang middle school told Shanghai news portal jiemian.com that they were waiting for a notice from the education bureau.

Shijiazhuang, capital of industrial Hebei province, registered airborne pollutants 100 times over WHO guidelines on Monday.

Some 460 million people are affected by the smog, Greenpeace said this week, or “a population equivalent to that of the U.S. Canada and Mexico combined’’.

Beijing’s levels of fine particulate air pollution, known as PM2.5, registered 420 micrograms per cubic square meter, according to the U.S. Embassy Air Quality Index.

The maximum safe level is 25, according to the World Health Organisation (WHO).