MOSCOW, August 4 (RIA Novosti) - A third man has died of pneumonic plague in northwest China, the Xinhua news agency said on Tuesday.

Pneumonic plague has already killed a 32-year-old herdsman and one of his neighbors, aged 37, in the town of Ziketan, in Xinghai county in the Hainan Tibetan Autonomous Prefecture, the Chinese agency said.

Local authorities quarantined Ziketan after the outbreak was reported on July 30 infecting nine people, most of them being relatives of the first victim. One of the infected is currently in a serious condition.

Meanwhile, no new infections have been reported.

According to the World Health Organization, pneumonic plague, which affects the lungs and can be transmitted from person to person or from animals to people, can be fatal within 24 hours of infection.

Russia's chief sanitary official, Gennady Onishchenko, warned on Monday that Russia would tighten controls on the Chinese border following the outbreak.