A second patient, a 39-year-old man from Dongguan, commuted to the district. The pair follow Tri Mawarti, a domestic helper who was the first person in Hong Kong diagnosed with the virus. She is believed to have handled a live chicken at a flat in Nanwan Street before falling ill.

Four people have been confirmed as having contracted the H7N9 virus in Guangdong in five days. The province has confirmed six cases since August; two in Dongguan , two in Yangjiang , one in Huizhou and yesterday's case.

Cheng Jinquan, the centre's director, said at a news conference that the second patient from Dongguan and the Hong Kong patient had been to Longgang district before falling ill.

"The 39-year-old Dongguan patient commuted to work in the Ganlan area in Longgang district in Shenzhen," Cheng said. "The Hong Kong domestic helper from Indonesia also travelled to Shenzhen in late November.

"There's no further evidence to prove they got infected in Shenzhen because both are still in a coma and could not give information," he said.

The Shenzhen patient saw a doctor on December 9 at a local clinic after developing a fever. He went to hospital on Thursday last week and was transferred to another clinic the next day with severe pneumonia.

Hong Kong's public hospitals have stepped up their bird flu tests on patients.

Hospital Authority chief executive Dr Leung Pak-yin said yesterday that all patients with pneumonia and flu-like symptoms were required to be tested for bird flu, even if they had not come into contact with birds or poultry or travelled recently.