A 36-year-old Indonesian maid is in hospital in critical condition, the southern Chinese financial hub's Health Secretary Ko Wing-man said late Monday.
The maid had a history of traveling across the border to the mainland city of Shenzhen to buy, slaughter and eat chickens, Ko said.
H7N9 was first identified April. It has sickened 139 people and killed 45 in China and Taiwan.
It appears to have stalled since Chinese authorities cracked down on live animal markets following the initial outbreak.
But scientists fear the virus will re-emerge in the winter, when influenza is most active.
Ko said the semiautonomous Chinese city's government would step up its flu pandemic preparedness plan. Infectious diseases are a particular concern in Hong Kong, where the 2003 outbreak of Severe Acute Respiratory Syndrome, or Sars, killed about 299 people. Nearly 500 more deaths were reported in other countries.