Dense smog has shrouded Beijing, China's capital, with pollution at hazardous levels for a second day, with residents advised to stay indoors, state media has said.
The municipal environment warning centre issued an alert on Saturday advising the elderly, children, and those suffering respiratory or cardiovascular illness to avoid going out or doing strenuous exercise, Xinhua reported.
Air quality in Beijing showed airborne particles with a diameter small enough to deeply penetrate the lungs at a reading of 456 micrograms per cubic metre, the warning centre said.
The quality is considered good when the figure stands at less than 100, but a reading shown on the website of the US embassy in the city was above 800.
Beijing only measures up to a maximum value of 500, with the US embassy tweeting that their own readings were "beyond index".
Those who ventured out had to wear facemasks for protection, with visibility low, the skyline shrouded, and the sun hidden in the smog.
Last year, Beijing said it was illegal for foreign embassies to issue their own air quality readings, but the US said its diplomatic missions in China would not stop tweeting levels, which were useful to its citizens living abroad.
More days of smog
The heavy pollution is expected to last another three days, with weather conditions preventing pollutants from dispersing, the warning centre said, according to Xinhua.
Yu Jianhua, head of the atmospheric environment management office of the Beijing Environmental Protection Bureau, said that current weather conditions in the capital are preventing the pollution from dispersing, as the temperature and humidity have kept mounting in the city recently.
Yu advised local residents to turn to public transportation in order to reduce pollution created by automobile emissions.
Fog also covered vast swathes of east and central China, with numerous closed highways and delayed flights in several provinces, it added.
China's air quality is among the worst in the world, international organisations say, citing massive coal consumption and car-choked city streets in the world's biggest vehicle market.
Formulated at the end of 2012, Beijing's emergency response plans for seriously-polluted days currently rank pollution into three levels, including polluted, seriously polluted and heavily polluted.