number of infected people had risen to seven, government officials said.
Worryingly, the cases have been reported from different parts of the country, increasing the chances of a country-wide outbreak. At least four cases were reported from different cities of the Jiangsu province.
Three women and one man from four cities in Jiangsu were in critical condition and undergoing emergency treatment, state media said.
The source of the infections remained unclear, a statement issued by the provincial health department said, adding that 167 people who had close contact with the four infected have not shown fever or respiratory problems so far, two major symptoms of the avian influenza.
"Statistics on pneumonia cases caused by unknown reasons will be reported daily in Shanghai where two people died from the first known human infections of the bird flu strain," the state-run Xinhua news agency reported quoting an official from the municipal government.
"The city government will also set up an expert team to evaluate the severity and risk of the H7N9 bird flu, to step up research on the virus, and to closely watch the infections and people who have been in contact with them," the Xinhua report said.
The health authorities in Jiangsu have designated 16 leading hospitals to accept new cases in a bid to offer better treatment and reduce the mortality rate.
"On Monday, the Shanghai Animal Disease Prevention and Control Center tested 34 samples of pig carcasses pulled from the Huangpu River running through the city and providing it drinking water. It found no bird flu viruses," state media reported.
Thousands of dead pigs were retrieved from the Huangpu River last month, sparking huge panic as well as satire among the public over tap water safety
"Whether the viruses are contagious between humans remains a critical issue, and if it is, it means the disease is dangerous to the general public," Liu Youning, a respiratory expert with the People's Liberation Army General Hospital told Global Times newspaper.
"The priority is to find the source and to find out if the influenza virus has mutated to become contagious among humans and what kind of medicine is effective against the virus," Liu said. "With all these uncertainties, the public should try to avoid contact with poultry or other livestock and all infected patients should be separated from the general public."