Chinese officials ordered all live poultry trade and public poultry markets in several cities including Shanghai to immediately shut down as two more cases of the H7N9 "bird flu" virus surfaced on Saturday.
Six people have died in the country from the virus so far and currently up to 18 people have been infected, with the latest two reported on Saturday.
The Xinhua news agency said authorities will slaughter birds at two live poultry markets in Shanghai and one in Hangzhou following the culling of 20,000 others.
Authorities in China and Hong Kong said they were taking extra precautions, although there have been no recent signs that the virus has been transmitted from human to human, Reuters reports.
However, as the Guardianreports Saturday, "Scientists are particularly concerned about two of the virus's traits. H7N9 does not show symptoms in infected birds, allowing it to spread rapidly without detection. It also seems to be mutating quickly, meaning it could become contagious among humans."
The new strain of bird flu has infected 18 people in China, all in the east. Six people have died in an outbreak that has spread concern overseas.
The World Health Organisation (WHO) said that 10 infected people were severe cases and two were mild cases. It reiterated there was no evidence of ongoing human-to-human transmission of the virus.
"More than 530 close contacts of the confirmed cases are being closely monitored. In Jiangsu, investigation is ongoing into a contact of an earlier confirmed case who developed symptoms of illness," the Geneva-based WHO said in a statement on Saturday.
There were no signs of panic in Shanghai, where four of the six people died, and people generally said they were not worried. But the culling, which has been widely publicised, did underline for some how close to home the issue had become.