Health authorities ordered the closure yesterday of two Shenzhen wet markets where the deadly H7N9 strain of bird flu was detected.
The wet markets are in the border city's Longgang district. Today all poultry markets there will be closed for disinfecting.
The two poultry markets were closed for seven days from yesterday in order to cull all birds in stock and to carry out sterilisation, according to the Longgang authorities.
They said a team was sent on Sunday to collect 50 samples from three Longgang markets, including the two infected markets, and three samples were found to be infected.
In Hong Kong, live-poultry imports from Shenzhen farms have been banned since December 2 after the city's first H7N9 case was diagnosed.
The city will, however, continue to buy birds from other parts of the mainland as the government refuses to widen the ban despite a growing fear of the virus spreading.
Secretary for Food and Health Dr Ko Wing-man said he had requested mainland health authorities conduct more sensitive blood tests on poultry at farms before exporting the animals to the border, where Hong Kong would run the tests as well.
"The plasma test is more sensitive than the quick [genetic] test we are now conducting on live chicken," he said. "It will be more accurate in testing any birds that have come into contact with the virus, even if the bird itself is not a carrier or infected case."
University of Hong Kong microbiologist Yuen Kwok-yung believes it is necessary to use the plasma test.
"The shortcoming of the genetic test is that it detects the virus only when the bird is releasing it," Yuen said. "It may not detect anything if the virus level is low."
On Wednesday, the Guangdong health commission announced it had found H7N9 in three samples taken from poultry stalls at two Longgang wet markets - Kangqiao and Henggang.
Kangqiao market manager Wang Xiaohua said reporters were scaring off other vendors' customers and suggested the woman at whose stall the infection was found shut the stall.
"We suggested that our chicken vendor suspend trading because the reporters had frightened customers and other vendors," Wang said. "The vendor shut the stall herself and carried away about 20 chickens."
The vendor closed her stall at 9am before the authorities later ordered her to shut it.
The woman said she bought all her live chickens from the Buji Poultry and Livestock Wholesale Market, about three kilometres from the Kangqiao facility.
Civic Party lawmaker Dr Kwok Ka-ki urged the government to suspend all live-bird imports from the mainland as a precaution, but Ko said the current ban on Shenzhen farms was "more than adequate".
"Although [mainland authorities] have detected the H7N9 virus in samples taken in two [Shenzhen] markets, there has not been evidence so far they are the sources of the two human cases in Hong Kong," he said.