These stunning pictures show how Beijing has been swamped by pollution in its most serious smog alert to date.
Schools have been closed and rush-hour roads are virtually deserted after authorities issued a 'red alert' smog warning.
The red alert - the most serious warning - was announced late on Monday. It means authorities have forecast more than three consecutive days of severe smog.
It looks set to remain in place until at least Thursday.
Read more: Dramatic pictures show how Chinese capital has been covered in hazardous pollution
Most of the pollution is blamed on coal-fired power plants, along with vehicle emissions and construction and factory work.
An online notice from the Beijing Municipal Environmental Protection Bureau said it issued the alert to "protect public health and reduce levels of heavy air pollution".
Along with school closures and limiting cars to driving every other day depending on the last number of their licence plate, a raft of other restrictions will seek to reduce the amount of dust.
Officials said extra subway trains and buses would be added to handle the additional strain on public transport.
Beijing was also shrouded in persistent smog for most of November, when power demand soared due to unusually cold weather.
While pollution in the capital improved slightly in the first 10 months of the year, heavy smog that can be seen from space regularly forces Beijing schools to suspend outdoor activities and can even prompt highway closures because of reduced visibility.
There have previously been stretches of severe smog that lasted more than three straight days. However, those had been forecast to last three days or less, so they did not trigger a red alert.
A study led by atmospheric chemist Jos Lelieveld of Germany's Max Planck Institute and published this year in Nature magazine estimated that 1.4 million people die prematurely because of pollution in China each year.
China, the world's biggest carbon emitter, plans to upgrade coal power plants over the next five years to tackle the problem, and says its emissions will peak by around 2030 before starting to decline.
While emissions standards have been tightened and heavy investments made in solar, wind and other renewable energy, China still depends on coal for more than 60 per cent of its power.