Chinese Facebook users are criticising a post by Mark Zuckerberg jogging through Beijing without a face mask.
"Kicked off my visit with a run through Tiananmen Square, past the Forbidden City and over to the Temple of Heaven," the Facebook founder said in a post.
The National Meteorological Centre reported that smog this week reached "dangerously high levels" in Beijing.
The Chinese capital has been plagued by recurring air pollution linked to lung damage and respiratory illnesses.
Local media reported that the air in Beijing on Friday pushed past 300 AQI on the Air Quality Index, a level deemed 'hazardous'.
