The bad air quality is predicted to last until Tuesday and will again directly impact the capital, Beijing.
The notice comes hard on the heels of last week's red alert warning
-- the first ever -- when the Air Quality Index (AQI) reached 250, 10 times higher than the World Health Organization's recommended levels.
A red alert is triggered when the government believes the air quality will surpass 200 -- deemed "very unhealthy" by the U.S. government -- and most likely stay that way for three consecutive days.
Measures include school and construction site closures, a number plate system that reduces cars on the road by half, and advice that the public wear masks and stay indoors as much as possible.
The four-level system was actually introduced in 2013, which has lead some observers to question why the alerts haven't been employed until now.
China has regularly come under fire for its lack of transparency about air quality index figures and its seeming unwillingness to implement a warning system for residents.
But things appear to be changing.
Last week locals had 12 hours notice. Today the warning came while Beijing's skies were still blue, giving people more time to prepare and possibly reduce their likelihood of being exposed to the toxic shroud.
After decades of relentless growth China is having to come to terms with its climate change responsibilities.
Despite massive investment in renewable energy, it is still heavily dependent on coal.
But the Chinese leadership has vowed to crack down on pollution and cut emissions in half by 2030.
China was also part of last week's landmark COP21 Paris agreement
, when 195 countries adopted a legally binding agreement to fight climate change, sending a clear global signal that the era of fossil fuels is over.