Residents of Beijing are reaching for their face masks and staying indoors as air pollution in the Chinese capital again climbs into the hazardous range.
The city is notorious for its air pollution but even by those standards, this winter has been pretty bad.
The ABC reports that air pollution in Beijing hit record levels two weeks ago - four times what would be the normal unsafe levels.
After a brief respite, the 25 million residents of city are again breathing in fetid air.
China's top leaders have acknowledged the problem, telling people it will take a long time to fix.
Residents are using a mobile phone app to compare the government's official reading with measurements from the United States embassy and decide whether it is safe to go outdoors.
The ABC reports particulates are drifting into Beijing from coal-fired power stations in Shanxi and inner Mongolia.
They get locked in by surrounding mountains and mix with the exhaust of 5 million cars.
"Such serious air pollution will of course have a major impact on the human body," said Professor Pan Xiaochuan from Peking University Medical School.
"There's a rising death rate, an increase in cardiovascular diseases and respiratory system diseases.
"This smog is an alert to the government. It needs to put in a greater effort combating car exhaust and fired coal emissions."
Factory closures ordered
Beijing on Tuesday ordered the temporary closure of 103 factories because of persistent, hazardous levels of smog.
Government-run companies and state agencies were also told to reduce their use of cars by a third.
The city has been smothered for days in a dense blanket of pollution caused by coal burning and factory and car emissions.
On Thursday, levels still hovered around the "very unhealthy" mark. Winds are forecast for Friday.