Five people have been diagnosed pneumonic plague in southwest China's Tibet Autonomous Region and one of them has died, health authorities confirmed Sunday.

All the five cases were reported in Latok Village, Nangxian County of Nyingchi Prefecture, Ministry of Health said on its website, quoting a report from Tibet's regional health department.

It said the first case was detected on Sept. 23 and the patient died of severe lung infection.

The other four cases, all of whom reportedly had direct contacts with the first patient, have been quarantined.

"One of the cases is critical and the other three appear in stable condition," the report said.

Health authorities did not identify the patients.

The health department in Tibet has sent disease prevention and control specialists to Nangxian County to prevent the epidemic from spreading further.

It said everyone who visited the county after Sept. 18 must immediately seek treatment should fever, cough or other flu-like symptoms appear.

Tibet has alerted all neighboring provinces to the cases.

Pneumonic plague, an infection in the lung, is a rare but deadly form of plague. Signs of illness include fever, headache, weakness and rapidly developing pneumonia.

In China plague is categorized as Class A infectious disease -- the most serious class under China's Law on the Prevention and Treatment of Infectious Diseases.

The most recent fatal case of plague in China was reported in June, according to the health ministry.