ABC's Jennifer Wu reports from Beijing: Officials have identified a patient afflicted with pneumonic plague as "near death" in northwestern China while another is in serious condition. Medics have scrambled to prevent further spread of the disease outbreak with thousands of people in Qinghai province quarantined. Three deaths have occurred so far, all in the town of Ziketan. The last was a 64-year-old man who died Tuesday. At least a dozen others have ended up in the hospital as well, confirmed with the plague. They reportedly are mostly relatives of the first victim, a herdsman who passed away over the weekend. Pneumonic plague, caused by airborne bacteria found in bubonic plague, can kill about 60 percent of those infected if left unchecked. The World Health Organization states that the disease is among the deadliest known as it spreads easily and can claim its victims within 24 hours of infection. Authorities have set up checkpoints and blockaded the town and its surrounding areas within a 17-mile radius. A number of residents though have tried to flee the city out of fear. It is unconfirmed how many have succeeded. Meanwhile health officials continue to disinfect the area and kill rats, insects, and other viable carriers of the plague. The Qinghai health bureau has urged for any visitors to Ziketan and neighboring areas since last month to seek treatment right away if they show any sign of a fever or cough.