Hong Kong Wednesday reported its third death from H7N9 bird flu -- an elderly man who had visited mainland China -- a day after authorities culled 22,000 birds to curb the disease.

The 75-year-old man had previously travelled to the neighbouring Chinese city of Shenzhen and died Wednesday morning, a government doctor told reporters.

"Today we have confirmed the fourth H7N9 in Hong Kong, this case is likely to be an imported infection," Doctor Chuang Shuk-kwan of the Centre for Health Protection told reporters.

Chuang said the man had travelled alone to the neighbouring mainland Chinese city of Shenzhen from January 20 to 26.

"He stayed in a residence in the Bao'an district and there are live poultry markets around that area," she said.

He was admitted to the intensive care unit of Hong Kong's Tuen Mun hospital on Tuesday afternoon with a high fever.

"We obtained some samples from his respiratory tract after he had been admitted to the hospital. After he died, we discovered it was H7N9," Chuang said.

"Because of the geographic proximity there's no way we can stop human traffic between mainland and Hong Kong," health minister Ko Wing-man said, adding that residents travelling to the mainland should wear masks and wash their hands frequently if they visit wet markets.

Fears over avian flu have grown following the deaths of two men from the H7N9 strain of the virus in Hong Kong since December.

A 65-year-old man died on January 14 and an 80-year old man died on Boxing Day last year. Both had recently returned from mainland China.

The latest case comes a day after the city culled thousands of birds, mainly chickens, following the discovery of infected poultry imported from the mainland.

Officials wearing masks and protective suits piled dead chickens into black plastic bags Tuesday, at Hong Kong's Cheung Sha Wan market where the virus was found.

Cheung Sha Wan -- Hong Kong's only wholesale poultry market --- is now shut for 21 days for disinfection and the sale of live birds in the city has ground to a halt on the eve of the Lunar New Year holiday season.

So far this year, China has confirmed 110 human H7N9 cases including 22 deaths, according to an AFP tally of reports by local authorities.

In the worst-hit province of Zhejiang, three members of the same family contracted the H7N9 strain, the official Xinhua news agency reported late Tuesday.

Hong Kong health authorities said a total of 254 H7N9 cases have been confirmed on the mainland since the outbreak began there in February 2013, sparking fears the virus could mutate to become easily transmissible between people, potentially triggering a pandemic.

An additional four cases have been confirmed in Hong Kong, three of them fatal.