China reported on Tuesday that four more people in one province were seriously ill with a bird flu virus new to humans, following two previous deaths.

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The health bureau of eastern Jiangsu province said in a notice on its website that three women, aged 45, 48 and 32, and an 83-year-old retired man, from different cities in the province, were all critically ill with the H7N9 virus, a diagnosis confirmed by the provincial disease prevention centre.

Based on the bureau's statement, only one of the patients appeared to come into daily contact with birds - the 45-year-old woman, who was described as a poultry butcher.

The four cases did not appear to be connected, and people who have had close contact with the patients have not reported having fevers or respiratory problems, it said.

The provincial health bureau said it was strengthening measures to monitor suspicious cases and urged the public to stay calm, joining Beijing and China's financial capital, Shanghai, in rolling out new steps to respond to the relatively unknown virus.

The four latest cases follow three earlier ones reported on Sunday, including two men who died in Shanghai, resulting in the city activating an emergency plan that calls for heightened monitoring of suspicious flu cases.

Under the contingency plan, schools, hospitals and retirement facilities are to be on the alert for fevers, and administrators are to report to health authorities if there are more than five cases of flu in a week.

Cases of severe pneumonia with unclear causes are to be reported daily by hospitals to health bureaus, up from the weekly norm. The plan also called for stronger monitoring of people who work at poultry farms or are exposed to birds.

The level-3 response plan, the second-lowest in a four-stage scale, reflects higher concern after the H7N9 bird flu virus led to the deaths of two men in Shanghai and seriously sickened a woman in the city of Chuzhou 230 miles west.

"The health bureau will take effective and powerful measures to prevent and control the disease, to make sure the flu epidemic is effectively guarded against and to safeguard the health of the city's residents," said Xu Jianguang, head of the Shanghai Health Bureau.

The H7N9 strain, so named for the combination of proteins on its surface, has previously been considered not easily transmitted to humans, unlike the more virulent H5N1 strain, which began ravaging poultry across Asia in 2003 and has since killed 360 people worldwide.

Health officials said this week there was no evidence that any of the three earlier cases, who were infected over the past two months, had contracted the disease from each other, and no sign of infection in the 88 people who had closest contact with them.

Health authorities in Beijing also upped the capital's state of readiness, ordering hospitals to monitor for cases of bird flu and pneumonia without clear causes, the official Xinhua News Agency reported.

The announcements, as lacking in details as they are, show that the government is mildly more transparent in handling health crises than it was a decade ago during the SARS pneumonia epidemic. Then, as rumours circulated for weeks of an outbreak of an unidentified disease in southern Guangdong province, government silence contributed to the spread of the virus to many parts of China and to two dozen other countries.