BEIJING, May 10 (Reuters) - China's agriculture ministry said on Thursday it had called on local governments to report all new cases of a disease that some industry officials estimate has wiped out as many as a million pigs in China in the last year.

The move follows an outbreak last month near Yunfu city in the southern Guangdong province that state media said led to death of some 300 pigs.

"It is the season for peak outbreaks. High temperature and humidity could cause even more outbreaks in the summer and autumn," the ministry said in a notice published on its Web site (www.agri.gov.cn).

Officials have had difficulty determining precisely how widespread the disease has become because it had not been identified in earlier outbreaks and because of the disperse nature of China's pig industry, with many animals raised on small farms or by individual farmers.

The ministry has not said how many pigs have died from the disease since the first outbreak was reported a year ago in south Jiangxi province. But industry officials say the disease is now prevalent across the country, with estimates of pig deaths ranging from half a million to 1 million.

The disease, caused by a variation of the Porcine Reproductive and Respiratory Syndrome (PRRS) virus, does not affect people, but the new strain has a higher mortality rate, said the ministry.

The ministry has successfully worked out a new type of vaccine against the disease and would speed up production to apply to pigs in some key suffering areas, it said. It did not elaborate.

The disease causes stillbirths in pigs, fever, loss of appetite, diarrhoea and redness of the skin. The ears of the affected pigs turn temporarily blue.

It could not be identified during its earlier outbreaks and was known in the feed industry as "unidentified high fever disease".

Mortality rates of as high as 50 percent had led farmers to abandon breeding and the reduction of the pig population has caused a heavy blow to the feed industry.

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