A Chinese city has been sealed off and 151 people placed in quarantine since last week after a man died of bubonic plague, state media said Tuesday.

The 30,000 people living in Yumen in the northwestern province of Gansu are not being allowed to leave, and police at roadblocks on the perimeter of the city are telling motorists to find alternative routes, state broadcaster China Central Television (CCTV) said.

The 38-year-old victim died last Wednesday, the report said, and had been in contact with a dead marmot, a small furry animal which lives on grasslands and is related to the squirrel.

"The city has enough rice, flour and oil to supply all its residents for up to one month," the report added.

"Local residents and those in quarantine are all in stable condition."

CCTV said "authorities are not allowing anyone to leave", although a previous report by the China Daily newspaper said "four quarantine sectors" had been set up in the city.

No further cases had been reported by Tuesday.

Plague is categorized as a "Class A infectious disease" in China, a report by the official news agency Xinhua said, "the most serious under China's Law on the Prevention and Treatment of Infectious Diseases".

Bubonic plague is a bacterial infection most well known for the "Black Death", a virulent epidemic of the disease that killed tens of millions of people in 14th-century Europe. Primarily an animal illness, it is extremely rare in humans.

The US Centers for Disease Control (CDC) says on its website that modern antibiotics are effective in treating plague, but that without prompt treatment, the disease can cause serious illness or death.

"Human plague infections continue to occur in the western United States, but significantly more cases occur in parts of Africa and Asia," it adds.