A sixth person has died of H7N9 bird flu in China, state media said Friday, after authorities culled poultry at a Shanghai market where the virus was detected.
The 64-year-old farmer died in Huzhou, in the eastern Chinese province of Zhejiang, local officials said according to the official Xinhua news agency.
He is thought to be among 14 human cases of H7N9 that were previously confirmed, and is the second person from the Zhejiang to die from the strain, with the other four fatalities coming from the commercial hub of Shanghai.
Authorities in Shanghai were also monitoring a person who had been in close contact with one of the dead, who was being treated for flu-like symptoms, while US officials said they were looking to develop a vaccine.
The first two deaths from the virus, which had not been seen before in humans, occurred in February but were not reported by authorities until late March. Officials said the delay in announcing the results was because it took time to determine the cause of the illnesses.
According to the World Health Organization (WHO), the animal source of the infection and its mode of transmission are not yet clear.
"We do not yet know enough about these infections to determine whether there is a significant risk of community spread," the UN's health agency stated in an online H7N9 update.
Experts are concerned that the virus appears to have spread across a wide geographical area, not only in Shanghai, but also the nearby provinces of Zhejiang, Jiangsu and Anhui.
"I am cautiously worried," virologist John Oxford of the Queen Mary University of London told AFP.
"If there were four cases in Shanghai, I would be much less concerned, but because it is so geographically widespread I think it is trying to tell us something."
US health authorities said Thursday they were liaising with domestic and international partners to develop a vaccine for the virus.
The Centers for Disease Control and Prevention, a US federal agency, said it was "gathering more information to make a knowledgeable public health risk assessment, and developing a candidate vaccine virus".
State broadcaster China Central Television (CCTV) reported Friday that health ministry officials were meeting with agricultural personnel to draw up an action plan aimed at "preventing the spreading of the disease".
The poultry cull was carried out at the Huhuai market in a western suburb of Shanghai following the discovery of the virus in pigeon samples, Xinhua reported.
Images posted on Sina Weibo by a local television reporter Friday showed men wearing full protective clothing and facemasks entering the market during the night.
Some images showed birds in plastic cages, while others showed dozens of empty birdcages stacked in the middle of the market.
On Friday morning, the entrance to the poultry section was concealed with wooden boards and sealed off with plastic tape, with a police car parked nearby and white disinfectant powder sprinkled in the street.
Vegetables remained on sale at the facility, where customers continued to shop for their daily groceries.
Two staff members at the market told AFP the slaughter was completed overnight, but one of them, a worker at the customer service centre, added: "Of course, I'm worried."