The 64-year-old man was a neighbour of the first two people to die from the plague in Ziketan in Qinghai Province.

Police have set up checkpoints around Ziketan, as medics are disinfecting the area and killing rats and insects.

Pneumonic plague, which attacks the lungs, can spread from person to person or from animals to people.

A spokeswoman for the World Health Organization, Vivian Tan, earlier said an outbreak such as this was always a concern, but praised the Chinese for reacting quickly and for getting the situation under control.

Local officials in north-western China have told that the situation is under control, and that schools and offices are open as usual.

But to prevent the plague spreading, the authorities have sealed off Ziketan.

About 10 other people inside the town have so far contracted the disease, according to state media.

No-one is being allowed leave the area, and the authorities are trying to track down people who had contact with the men who died.

Initial symptoms of pneumonic plague include fever, headache and shortness of breath.

The local health bureau has warned anyone with a cough or fever who has visited the town since mid-July to seek medical treatment.

According to the WHO, pneumonic plague is the most virulent and least common form of plague.

It is caused by the same bacteria that occur in bubonic plague - the Black Death that killed an estimated 25 million people in Europe during the Middle Ages.

But while bubonic plague is usually transmitted by flea bites and can be treated with antibiotics, pneumonic plague is easier to contract and if untreated, has a very high case-fatality ratio.