Schools were closed, building work suspended and restrictions on cars were put in place in Beijing on Tuesday after the Chinese capital issued its first-ever “red alert” for smog.
There have been some improvements in air quality in Beijing in the past year, but readings of the most dangerous particles, PM2.5, were up to 12 times the level considered safe.
Under the alert, schools were initially advised to voluntarily close unless they had good air purification systems, before the education ministry ordered all schools shut until Thursday.
The ministry of environmental protection ordered reinforced measures against the smog, the Xinhua news agency reported, while praising “the prompt response in the hazy capital”.
China has reduced emissions and invested in renewable energies such as solar power or wind, but the country still depends on coal for more than 60 per cent of its power.
"Environment authorities must closely follow the situation, improve monitoring and forecasting, and guide local governments' emergency response plans," environment minister Chen Jining told a news conference.
Mr Chen said the warning levels should be adjusted according to the real-time pollution conditions.
The air quality index was still at 308, a “severely polluted” reading, by 5pm local time. The smog was predicted to last three more days.
The ministry also sent two teams to the central province of Henan to inspect measures to cope with the severe pollution, Xinhua said.
It had previously dispatched 10 inspection teams to regions known for heavy pollution, mainly around Beijing, to ensure emergency plans were in place. The teams also monitored known polluters, such as those that burn coal and high-emission vehicles.
Other measures included limiting cars to driving every other day depending on the last number of their number plate. Extra subway trains and buses would be added to help cope with the additional strain on public transport.
"The red alert is a welcome sign of a different attitude from the Beijing government," said Greenpeace Asia's climate and energy campaigner Dong Liansai. "However, this, the latest of a series of airpocalypses to hit Beijing, is also a firm reminder of just how much more needs to ensure safe air for all."