China has increased precautions in Bayannur, a city in the Inner Mongolia autonomous region, after one confirmed case of bubonic plague.
It is not clear they might have become infected.
Another suspected case involves a 15-year-old, apparently getting it from a marmot hunted by a dog.
It has been given a level 3 alert, which forbids hunting and eating animals that could carry the plague. The public have been asked to report suspected cases.