Just days after Hong Kong health workers slaughtered 2,700 poultry after excrement samples tested positive for the deadly strain of H5N1 avian influenza virus, the city officials on Wednesday ordered the slaughter of all chickens in the city’s markets and retail outlets.

The decision was taken as a precaution after tests showed birds infected in four markets, Agriculture, Fisheries and Conservation Director Cheung Siu-hing said on Wednesday, Reuters reports.

The number of birds that will be killed is not known yet, but there are no less than 64 markets in Hong Kong.

The presence of bird flu in Hong Kong made the authorities to immediately ban all live chicken imports from mainland China, the main source of poultry in the densely populated city.

No human cases of avian influenza has been signaled so far but authorities “will remain alert,” Thomas Tsang, head of the government’s health monitoring agency, said.

The bird flu virus began ravaging Asian poultry stocks in late 2003. According to the World Health Organization, there have been 382 human cases worldwide since 2003, 241 of them fatal. Indonesia is the hardest hit regions of all, with 108 of the deaths and is seen by health experts as a potential hotspot for a pandemic.

The last time Hong Kong confronted with a major bird flu outbreak was back in 1997, when the virus jumped to humans and killed six people. Nearly 1.5 million birds were slaughtered at the time. The virus appeared again last year but only in wild birds.