Eleven of the 43 people found to be infected with bird flu in China have died, the World Health Organization said Friday.
The latest to succumb was a patient from Shanghai.
Of the five latest cases to be confirmed by a laboratory, three are from Zhejiang and two from Shanghai. Their ages range from 53 to 86.
WHO said that more than a thousand close contacts of the confirmed cases are being closely monitored.
Seventy people have had close contact with three of the patients, but none of them have exhibited abnormal symptoms, according to a statement from the Shanghai Municipal Health and Family Planning Commission, cited by Xinhua news agency.
WHO said at present there is "no evidence of ongoing human-to-human transmission," but the international agency and Chinese health officials continue to keep their eyes on that.
"The Chinese government is actively investigating this event and has heightened disease surveillance," WHO said.
While the source of the infection is unknown, poultry markets have become the focus of the investigation by China's health ministry and the WHO. The virus involved, H7N9, had been known to affect pigeons but had not previously been discovered in humans until a series of cases were reported in China last week.
On Wednesday, the Chinese Academy of Sciences said the H7N9 virus probably came from migratory birds from East Asia that mixed with domestic fowl in China's Yangtze River delta region.
Several cities across eastern China have suspended trading in live poultry in an effort to contain the problem.
On Friday, Hong Kong's Food and Environmental Hygiene Department announced that poultry imported from companies in mainland China would be subjected to "fast tests" for the H7N9 and H5N1 strains of the virus.
According to a statement, "Officers will randomly select 30 birds from each consignment of around 1,000 (birds), to collect swabs and blood samples for the rapid test detecting the H5 and H7 antigen and antibodies."
Results will available within five hours, with cleared poultry then taken to a temporary wholesale market in the city for sale.
"When there are birds infected by H7 or H5, all the import of poultry will be suspended according to the World Organization for Animal Health's recommendations," said Allen Chan, senior veterinary officer with the city's health department.
The current outbreak has started to take its toll economically, after Yum Brands, the parent company of KFC in China, warned this week that sales at its restaurants across the country had suffered a sharp fall.
Xinhua also reported that the price of poultry had fallen by up to 50% in some eastern cities in the past week, hurting farmers economically. Shanghai has now completely banned the sale of life poultry.
CNN's Pamela Boykoff in Hong Kong and Ke Feng in Beijing contributed to this report.