Hong Kong officials say they have confirmed the city's first case of deadly bird flu for this winter season.

A 68-year-old women remains in critical condition in the hospital where she was admitted after becoming ill Dec. 19, the city's government said in a statement.

Health officials say they have classified her case as "imported," finding she had recently returned from the city of Shenzhen in mainland China's southern Guangdong Province, site of the first reported case of the deadly H7N9 bird flu strain in March 2013.

While in Shenzen the woman, currently in intensive care in the city's Tuen Mun Hospital, dined on "home-cooked" chicken, authorities said, but she experienced no exposure to live poultry.

In 2013 the bird flu strain spread to Hong Kong and resulted in the deaths of three people.

In response to the new confirmation of H7N9 in the woman, Hong Kong's influenza pandemic response level was raised to "serious," up from "alert" and one step below "emergency."

As part of that response, city hospitals were taking measures to detect and contain any possible influenza infection by limiting visiting hours and requiring visitors to wear surgical masks.

Five women who were in a ward with the patient when she was admitted to Tuen Mun Hospital have been isolated and officials were attempting to track down her family members as well as two friends who had dinner with her in Shenzhen, said Secretary for Food and Health Dr. Ko Wing-man.

Ho advised city residents to avoid live poultry, although officials said sales of both imported and local live poultry in the city would not be affected.

On Dec. 7 authorities in Guangdong reported that a 66-year-old man died from the H7N9 virus 4 days earlier, the province's first confirmed fatality from the virus this winter.

"H7N9 cases have been moving south," Ko said. "We expect to see more imported H7N9 cases."

"We will closely monitor the situation... then decide the appropriate measures," he said.