Hong Kong (CNN) -- Two more people have died from a rare strain of bird flu in China, as health officials investigate possible cases of transmission between family members.
The latest fatalities occurred in Anhui and Jiangsu provinces -- both in eastern China -- and brought the total number of deaths from H7N9 avian influenza to nine, from 28 reported cases, according to the state-run Xinhua news agency.
So far the virus has been limited to the east of the country, with infections reported in the Shanghai region, as well as in the provinces of Anhui, Jiangsu and Zhejiang.
A total of 13 cases, including five resulting in fatalities, have been reported in Shanghai alone, where the authorities are considering a permanent ban on the trading of live poultry after culling more than 100,000 birds in the past week in an effort to contain the problem.
While the source of the infection is unknown, poultry markets have become the focus of the investigation by China's health ministry and the World Health Organization (WHO). The virus 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.
Other cities across China have announced plans to suspend trading in live birds. Authorities in the city of Nanjing took this a step further by announcing a ban on the trading of livestock and live poultry would come into effect from midnight on Tuesday, according to a statement from the Nanjing Urban Management Bureau -- though the WHO says no positive samples of the H7N9 virus have been found in pigs or farms in China so far.
Meanwhile, the WHO is investigating suspected "family clusters" of people who may be infected with H7N9, potentially the first evidence of its spread between humans.
"At this point, there is no evidence of sustained human to human transmission," said WHO spokesperson Gregory Hartl, in quotes carried by Xinhua. But he added that there are some "suspected but not yet confirmed cases of perhaps very limited transmission between close family members."
According to Hartl, one of the suspected family clusters was in Shanghai, with three family members having similar symptoms and one of them being confirmed of H7N9, Xinhua said. Two -- one confirmed and one suspected H7N9 case -- have now died, Hartl said. The other suspected cluster is in Jiangsu.
However Hartl cautioned that even if an infection is confirmed in another family member, further investigations would be required to ascertain whether it is actually a human-to-human transmission between constant and close contacts or a viral infection from the same environmental source, Xinhua said.
Despite assurances Tuesday from Vice Premier Liu Yandong that every effort would be made to prevent the spread of infections, Chinese netizens were taking to social media to voice their fears.
"I graduated from junior high school when there was an outbreak of SARS, then I graduated from high school and there was an H1N1 outbreak. Well, now I graduated from college and there is an H7N9 outbreak...... this generation has seen it all!" @Welly Han declared on Weibo, China's Twitter-like micro-blogging service.
Another, known as @Zhulin, posted: "At this point (H7N9 influenza), not going out would be a wise choice."
CNN's Ke Feng in Beijing contributed to this report.