The disease has proved so deadly that more than a quarter of the 67 confirmed cases in the southwestern province of Sichuan have died.

"Experts have initially diagnosed that the disease is caused by streptococcus suis bacteria infection," said a statement on the ministry's website.

"The direct cause of human infection of the streptococcus suis bacteria is the slaughtering or processing of infected pigs," it said. "No human-to-human infection has been found."

Sixty-seven confirmed cases and 13 suspected cases of the disease had been reported as of noon Sunday, including 19 fatalities, the statement added.

An emergency investigation by a group of experts organised by the ministries of health and agriculture found that the farmers infected had all slaughtered pigs found to have the disease, the China Daily reported.

Seventeen people remain in a critical condition while four have recovered. Symptoms of the disease included high fever, nausea, vomiting and haemorrhaging. About half of all patients go into severe shock.

Chinese reports said the cases were scattered among 75 villages in Ziyang and Neijiang cities.

The statement said officials have done all they can to minimise the number of deaths and have ordered villagers to stop slaughtering or processing infected dead pigs.

They were also working on an epidemic analysis, destroying infected pigs and eradicating contagious channels.

The disease is rare with the first recorded case found in Denmark in 1968. More than 200 cases of human infection have been reported globally since then.

To prevent the disease from spreading, pork exports from the affected cities have been halted, Hong Kong's Health, Welfare and Food Bureau said.

Hong Kong imports 30,000 tonnes of frozen pork from Sichuan province annually, although officials insisted there was no need to ban pork imports from other Chinese cities and inspection procedures were sufficient.