Pneumonic plague is a highly infectious, air-born form of the disease and is spread human-to-human through coughing. If left untreated, it can kill within 24 hours of infection, according to the World Health Organization (WHO).

In most cases, the pneumonic form is due to a secondary spread from an advanced infection of the bubonic plague, which is spread through flea bites.

'Provincial, prefecture and county-level health professionals are continuing to carry out disinfection and pest and rodent control, in order to eliminate fleas,' the Qinghai health bureau said in the statement.