China has announced a sixth death from a new bird flu strain, while authorities carried out the slaughter of all poultry at a Shanghai market where the virus was detected in pigeons being sold for meat.
The mass bird killing on Friday is the first so far as the Chinese government responds to the H7N9 strain of bird flu, which has sickened 16 people, many critically, along the eastern seaboard in its first known infections of people.
The first cases were announced on Sunday.
Health officials believe people are contracting the virus through direct contact with infected fowl.
Gregory Hartyl, spokesman for the World Health Organisation (WHO), said that the risk of the virus being spread between people was still a cause for concern.
"We may be seeing very few isolated cases of limited human-to-human transmission," Hartyl told Al Jazeera from Geneva, Switzerland.
Hartyl said that WHO was following up more than 500 contacts in regards to the virus.
"Of these now 16 confirmed cases that we have, and now these over 500 contacts, a couple of them do have signs of fever, or of runny nose, or of other flu symptoms, which means that until we know exactly what's happened with these contacts, we wouldn't want to say that there's no human-to-human transmission," Hartyl said.
"What we would say, however, is that it's very limited if there is."
Potential global pandemic
Scientists are watching closely to see if the flu could potentially spark a global pandemic.
The Agriculture Ministry confirmed late on Thursday that the H7N9 virus had been detected in live pigeons on sale at a produce market in Shanghai.
The killing of birds at the Huhuai market started on Thursday night after the city's agricultural committee ordered it in a notice also posted on its website.
State media on Friday ran pictures of animal health officials in protective overalls and masks working through the night at the market, taking notes as they stood over piles of poultry carcasses in plastic bags.
The area was guarded by police and cordoned off with plastic tape.
Experts urged Chinese health authorities to keep testing healthy birds, saying the H7N9 virus can infect birds without causing disease, making it harder to detect than the H5N1 bird flu virus that is more familiar to Asian countries.
H5N1 set off warnings when it began ravaging poultry across Asia in 2003 and has since killed 360 people worldwide, mostly after close contact with infected birds.