The death toll from an outbreak of pneumonic plague in northwest China has risen to three, state media reported on Tuesday as health officials maintained a quarantine lockdown on a town of 10,000 people.
The latest victim was a 64-year-old man who died on Monday in Ziketan, a remote town in a Tibetan area of Qinghai province where two fatalities had previously been reported, the Global Times said.
At least nine other people were infected with the highly-virulent disease - most of them relatives of the first victim, a 32-year-old herdsman, reports said, quoting local health authorities.
Qinghai provincial health authorities refused to comment when contacted by AFP on Tuesday.
Ziketan, which is about 200 kilometres (125 miles) southwest of the provincial capital Xining, had enough supplies to get by on its own for the time being, the official Xinhua news agency said.
Health authorities were urging people who had visited Ziketan on or after July 16 to seek immediate help if they developed a cough or fever.
Medical staff were tracking down people who had been in close contact with the patients but there had been no reports of new infections, Xinhua said.
The World Health Organization said the outbreak was a concern but hoped it could be contained as previous outbreaks in the same area had been in recent years.
"It's definitely a concern because this is probably the most lethal form of plague there is," WHO spokeswoman Vivian Tan told AFP in Beijing.
"But it is happening in a remote area of the country and the authorities seem to be taking the right measures so it's probably too soon to say how serious the situation is."
Tan said the bacteria which causes the plague is endemic in some rodents in the region.
"If the fleas from those animals do bite human beings they could lead to the bubonic plague, which is more common, and if that is left untreated it could sometimes lead to the pneumonic plague which we're seeing in Qinghai at the moment," she said.
However, Tan said there had been no reports of bubonic plague in the region, and the cause of the outbreak was unclear.
"At this point the authorities are still investigating so we can't really pinpoint the source of the problem," she said.
The vast high-altitude area is sparsely inhabited, mainly by Tibetan herders.
Plague in the region is mainly due to the handling of carcasses of infected rodents such as marmots, which are hunted for food and fur, the WHO says.
Pneumonic plague spreads through the air, making it easier to contract than bubonic plague, which requires that a person is bitten by an infected flea.
The WHO says pneumonic plague is the most virulent but least common form of plague. The mortality rate is high and patients can die 24 hours after infection.