Four new patients in China's eastern Jiangsu province have contracted a new strain of bird flu and were all in critical condition, the state news agency Xinhua has said.
Three women and a retired man from different cities in the province were all critically ill with the H7N9 virus, a diagnosis confirmed on Tuesday by the provincial health officials.
All of the new patients have been sick since about March 19, when they had fevers, coughs and other flu-like symptoms, the Jiangsu health bureau said in a statement.
Their conditions worsened over periods of time ranging from a week to 11 days and they were transferred to intensive care units in the provincial capital, Nanjing.
Based on the statement, only one of the patients appeared to have had daily contact with birds. One of the female patients was described as a poultry butcher.
The four cases did not appear to be connected, and other people who have had close contact with the patients have not reported having fevers or respiratory problems, it said.
The cases are the second batch to be confirmed after three in Anhui province and nearby Shanghai on Sunday.
The strain has already killed two people, raising the total number of known cases to seven.
The two deaths were men in Shanghai aged 87 and 27 who fell sick in late February.
The World Health Organisation (WHO) had said there was no evidence that the H7N9 strain could be transmitted between people, but that it was investigating the outbreak.
A woman in Anhui province who caught the virus in early March is also in critical condition.
New flu strain
In Hong Kong, health officials have urged vigilance over the new flu strain previously unknown in humans.
Leung Ting-hung, Hong Kong's top official responsible for disease prevention, said the government is closely monitoring the latest developments.
"From the information we obtained from the World Health Organisation as well as from the mainland, we noticed that this H7N9 virus is avian flu virus. Obviously, it has been, undergone, some kind of mutation so that it now can infect human beings," said Leung.
Hong Kong saw the world's first case of H5N1 avian flu in 1997. The outbreak, that killed six, was contained after authorities culled about 1.5 million chickens.
But the new H7N9 variation is not highly pathogenic or deadly among birds, Leung said.
"H7 is usually a low pathogenic virus. In other (words), it's less likely to kill birds or chicken. The main implication is we may not see a large number of deaths among birds or chickens, and then cases of, human cases, appear," Leung said.
Clinical virologist and Hong Kong University professor, Malik Peiris, who helped to identify the SARS virus in 2003, said the source of the infection had to be identified.
"Most of the people in close contact with these people have not got infected. So, it doesn't seem to be highly transmissible. But clearly, this has to be investigated," he said.