The two patients are being treated in Beijing Chaoyang Hospital having been diagnosed with the severe condition at noon today, China Global Television Network report. Prevention and control measures have been implemented. According to the World Health Organisation (WHO) the pneumonic plague can be fatal if left untreated and is extremely contagious.
From 2010 to 2015, 3248 cases were reported worldwide, including 584 deaths.
Pneumonic plague is also referred to as lung-based plague, as it is a severe lung infection.
WHO warn the disease can be transmitted via droplets to other humans and if not diagnosed and treated early, it can be fatal.
But the international health organisation say that recovery rates are high if detected and treated in time, usually within 24 hours of the onset of symptoms.
Typical symptoms include the suden onset of fever, chills, head and body aches, vomiting and nausea.
The incubation period is typically one to six days, but can be for as long as nine days.
The plague is caused by the bacteria Yersinia pestis, which is usually found in small mammals and their fleas.
Humans can become infected by the bite of infected flea, unprotected contact with infectious bodily fluids or contaminiated materials, or through contact with another infected patient.
Pneumonic plague is just one form of plague infection, with bubonic plague being the most common form.
The bubonic plague is caused by the bite of an infected flea, causing the lymph node to become inflamed, tense and painful.
At advanced stages of the infection the inflamed lymph nodes can turn into open sores filled with pus.
Bubonic plague can then spread to the lungs and advance to pneumonic plague.