According to China's state-run Global Times newspaper, the first case was 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, reports the BBC.
The second suspected case involved a 15-year-old, who had apparently been in contact with a marmot hunted by a dog, a tweet from Global Times said.
A level 3 alert, which forbids the hunting and eating of animals that could carry plague and calls on the public to report suspected cases, has been put in place until the end of the year.
Bubonic plague, caused by bacterial infection, was responsible for one of the deadliest epidemics in human history - the Black Death - which killed about 50 million people across Africa, Asia and Europe in the 14th Century, the BBC report said.
There have been a handful of large outbreaks since.
It killed about a fifth of London's population during the Great Plague of 1665, while more than 12 million died in outbreaks during the 19th Century in China and India.
But nowadays it can be treated by antibiotics. Left untreated, the disease, which is typically transmitted from animals to humans by fleas, has a 30-60 per cent fatality rate.
Symptoms of the plague include high fever, chills, nausea, weakness and swollen lymph nodes in the neck, armpit or groin.
Bubonic cases are rare, but there are still a few flare-ups of the disease from time to time.
Madagascar saw more than 300 cases during an outbreak in 2017. However, a study in medical journal The Lancet found less than 30 people died.
In May 2019, two people in the country of Mongolia died from the plague, which they contracted after eating the raw meat of a marmot - the same type of rodent the second suspected case came into contact with.
The bubonic plague report comes as the world is struggling to contain the ongoing COVID-19 pandemic which originated in China's Wuhan city last December.
On Monday morning, the total number of cases stood at 11,409,805, while the fatalities rose to 533,684, according to the Johns Hopkins University.