Two people have died from the H7N9 strain of bird flu in China's commercial hub Shanghai, including a medical doctor, the local government said Monday, the city's first fatalities from the virus this year.

The victims included a 31-year-old surgeon who worked at the Shanghai Pudong New Area People's Hospital, the city health commission and hospital said, but gave no details on how he was infected.

Local media said the doctor worked in the emergency room and kept reporting for duty even though he experienced a fever for a week. He left a pregnant wife, the Shanghai Daily newspaper reported.

The other victim was a 77-year-old man, described as a farmer, the Shanghai Health and Family Planning Commission said in a statement.

Shanghai had registered seven cases of bird flu so far this year, it said.

The H7N9 human outbreak began in China in February 2013 and reignited fears that a bird flu virus could mutate to become easily transmissible between people, potentially triggering a pandemic.

Cases and deaths dropped significantly after the end of June, but have begun to pick up with the onset of winter.

For last year as a whole, China had 144 cases, including 46 deaths, from H7N9 avian influenza, according to figures from China's National Health and Family Planning Commission.

So far this year there have been at least six deaths in mainland China, according to local announcements.

Two people have also died from the virus in Hong Kong since late December.

Chinese officials have so far ruled out the possibility of widespread human-to-human transmission of the virus but say limited transmission, such as spreading between family members in close contact, is possible.