China has confirmed a new case of the H7N9 bird flu, state media said, the country's first report since August of human infection with a virus that has so far afflicted 135 people.

A 35-year-old man in Shaoxing in China's eastern province of Zhejiang has been hospitalized with the virus and is in critical condition, the official Xinhua news agency said on Tuesday.

"Liu, a company employee from Shaoxing county, was admitted to a township hospital on October 8," the agency said.

China's National Health and Family Planning Commission said 45 people had died from the virus, which was first detected in humans early this year.

Zhejiang has recorded the highest number of H7N9 infections anywhere in China.

While there have been only a handful of H7N9 infections during the summer months after a surge in April, flu experts warn that the threat posed by the virus has not passed.

The first scientific analysis of probable transfer of the new flu strain between humans, published in the British Medical Journal in August, gave the strongest proof yet that it can jump between people, and so potentially cause a human pandemic.

Another study published in August identified several other H7 flu viruses circulating in birds that "may pose threats beyond the current outbreak".