Beijing, the Chinese capital with a population of 21 million people, issued its first red alert Tuesday morning due to the city's smog.

CNN reports Beijing's Municipal Bureau of Environmental Protection predicted the capital would be cloaked in severe pollution for several days.

The U.S. Embassy in Beijing measured the city's air quality index at 250 micrograms on Tuesday, which far exceeds the World Health Organization's recommended level of 25.

According to the Independent, the smog severely hindered visibility, with some residents unable to see beyond 200 meters in certain areas of the capital.

Resident Gao Yuanli, 35, told CNN that the pollution forced her to wear face masks during the winter and to purchase a personal air purifier.

"I can't go out on weekends now if the air is bad, and I don't go to outdoor markets anymore," she said.

With the alert came school closures and limited construction. Beijing also restricted driving, only allowing either even or odd numbered license plated vehicles to occupy roads at one time. Large cars and trucks were banned entirely.

Beijing's smog is generated by coal burning and heating, as well as dust accumulation from the city's various construction sites. High humidity and low wind only exacerbate the issue.

"The city is blanketed in a thick, choking smog that has covered an area of North China the size of Spain and Beijing's most famous landmarks have been completely obscured by the yellow haze," Zhang Kai wrote on Greenpeace's blog. The group called for the city to raise its orange alert to red in the midst of a four-day pollution spike they referred to as "Airpocalypse."

Some residents questioned why the red alert was being put in place now, as opposed to last week, which measured pollution levels at over 500. Others just saw the situation as evidence of everyday life in Beijing.

"I'd find a day when the sky is blue unusual," resident Wolf Hu said.