A rural herdsman tested positive for the infection, which can be treated with antibiotics.
Authorities in China have stepped up precautions after a city in the Inner Mongolia autonomous region confirmed one case of bubonic plague.
According to state reports, the Bayannur patient - a herdsman - is now in quarantine and in stable condition.
Officials issued a Level 3 warning, the second lowest in a four-tier system.
The bubonic plague, caused by bacterial infection, can be deadly, but can be treated with commonly available antibiotics.
The new case was first reported as suspected bubonic plague on Saturday at a hospital in Urad Middle Banner in Bayannur city.
It is not yet clear how or why the patient might have become infected.
The level 3 alert forbids the hunting and eating of animals that could carry plague and calls on the public to report suspected cases.
Fatal but treatable
Cases of bubonic plague are periodically reported around the world.
Madagascar saw more than 300 cases during an outbreak in 2017.
In May last year, two people in the country of Mongolia died from the plague - they had contracted the illness after eating the raw meat of a marmot, a type of rodent.
A World Health Organization official in Ulaanbaatar - the capital of Mongolia - had told the BBC that raw marmot meat and kidney was thought to be a folk remedy for good health.
The rodent is a known carrier of the plague bacteria and it is commonly associated with plague cases in the country. Hunting the rodent is illegal.
The bubonic plague is characterised by swollen lymph nodes. It can be hard to identify in its early stages because symptoms, which usually develop after three to seven days, are flu-like.
But it's unlikely the bubonic plague - infamously known as the Black Death - will lead to epidemic.
"Unlike in the 14th Century, we now have an understanding of how this disease is transmitted," Dr Shanti Kappagoda, an infectious diseases doctor at Stanford Health Care told news site Heathline.
"We know how to prevent it. We are also able to treat patients who are infected with effective antibiotics."
The Black Death caused about 50 million deaths across Africa, Asia and Europe in the 14th Century.
Its last terrifying outbreak in London was the Great Plague of 1665, which killed about a fifth of the city's inhabitants. In the 19th Century there was a plague outbreak in China and India, which killed more than 12 million. BBC