China’s still getting hit with intense levels of air pollution. As of Wednesday, Beijing was under a "red alert" for smog - the highest of four levels - and a "yellow alert" for fog.

Other areas, particularly in northern China were still under red alert as of Wednesday for both fog and smog.

This photo, by CNN chief national security correspondent Jim Sciutto, shows just how insane the smog has gotten, enveloping the capital so much that just the tops of the buildings can be seen.

The high pollution has been going on for a number of weeks, causing flight delays, and leading to traffic bans.

Colder temperatures means more coal is burned to heat homes, which exacerbates China’s air pollution problem.

Coal, and things like soot and dust, contain a particulate matter called PM 2.5.

The particulates are tiny, which makes it easy for them to get stuck in the lungs, leading to conditions like asthma and chronic lung disease.

As of Wednesday, the concentration of PM 2.5 in Beijing was 186 µg/m3 - seven times higher than what’s considered healthy.

Here’s a video showing the smog roll in on Sunday. The smog is expected to lift by the end of the week.

Beijing from the air as smog blankets the city. Just otherworldly - and alarming pic.twitter.com/P8oTLRFomR — Jim Sciutto (@jimsciutto) January 4, 2017

This article was originally published by Business Insider.

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