The health committee of the city of Bayan Nur issued the third-level alert, the second lowest in a four-level system.
The alert forbids the hunting and eating of animals that could carry plague and asks the public to report any suspected cases of plague or fever with no clear causes, and to report any sick or dead marmots.
Sunday's warning follows four reported cases of plague in people from Inner Mongolia last November, including two of pneumonic plague, a deadlier variant of plague.
The bubonic plague, known as the "Black Death" in the Middle Ages, is a highly infectious and often fatal disease that is spread mostly by rodents.
Plague cases are not uncommon in China, but outbreaks have become increasingly rare. From 2009 to 2018, China reported 26 cases and 11 deaths.
According to Xinhua, A 15-year-old resident of Ulaankhus soum was taken to a local hospital on Sunday after eating a marmot hunted by a dog, Dorj Narangerel, head of the ministry's public relations and surveillance department, told a press conference, urging people not hunt marmots or eat marmot meat.
Bayan-Ulgii is the westernmost part of Mongolia and shares borders with China and Russia.
Two cases of bubonic plague have recently been confirmed in the neighboring Khovd province.
Bubonic plague is a bacterial disease that is spread by fleas living on wild rodents such as marmots. It can kill an adult in less than 24 hours if not treated in time, according to the World Health Organisation.
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