Residents in Shijiazhuang, the capital of heavily industrialised Hebei province that surrounds Beijing, complained that schools were still open even though the city remained on red alert with air pollution levels close to record highs.

Media reports in central China’s Henan province also carried images of students taking exams in the smoggy open air.

“We already don’t know how long this smog will last, so why aren’t classes being stopped?” a Shijiazhuang resident posted on China’s Twitter-like Weibo microblogging service.

“The students are wearing masks every day and attending class in a daze, the windows are sealed shut and they don’t dare to ventilate and visibility is at just 20 metres,” the post said on Wednesday.

China began a “war on pollution” in 2014 amid concern its heavy industrial past was tarnishing its global reputation and holding back its future development. However, it has struggled to reverse the damage done by decades of breakneck economic growth, much of it based on the coal-burning power sector.

The air quality index (AQI) in the major steel-producing district of Fengnan in the Hebei city of Tangshan was still as high as 578 on Wednesday morning. Red alerts are issued when the AQI is forecast to exceed 200 for more than four days in a row, 300 for more than two days or 500 for at least 24 hours.

Chinese construction workers on an unfinished building in Beijing Tuesday, when the city issued a red alert, the most severe pollution warning, under which outdoor construction sites are advised to close (Photo: Reuters)

Concentrations of hazardous breathable particles known as PM2.5, another pollution gauge, were at a dangerous 380 micrograms per cubic metre. PM2.5 levels also remained high in Beijing, with average readings of 360 micrograms per cubic metre, according to official data. The safe recommended level of PM2.5 is 10 micrograms per cubic metre, according to the World Health Organization.

The Beijing-Tianjin-Hebei region, known as Jing-Jin-Ji, has been at the forefront of China’s efforts to cut pollution and has pledged to cut emissions of PM2.5 by 25 percent over the 2013-2017 period.

However, Guo Jinlong, Beijing’s top Communist Party official, told a government meeting on Tuesday the heavy smog could make it harder for the region to meet its annual targets.

He said more work was required to ensure emergency measures were implemented in full, according to an account of the meeting released by the Ministry of Environmental Protection.

The ministry has been naming and shaming companies in recent months for failing to cut output during bouts of smog, and it has also accused local authorities of monitoring lapses.

Many Beijing citizens have been blaming lax enforcement in other regions, including Shanxi and Inner Mongolia, China’s two biggest coal producers.

Researchers said on Wednesday that although around 30 percent of the PM2.5 in the Jing-Jin-Ji region this week had drifted in from other provinces, mainly Shandong and Henan, the bulk of pollution sources remained local.