Hong Kong's second case of the deadly H7N9 flu virus inside a week was confirmed last night. An 80-year-old Hong Kong man, who now lives in Shenzhen, was in a stable condition in Princess Margaret Hospital's isolation unit. The city's first case was confirmed on Monday. The patient, 36-year-old Indonesian domestic helper Tri Mawarti, remained in a critical condition in the same hospital last night. Zhejiang province yesterday also announced a new H7N9 case. The patient is a 30-year-old man from Anji county and he is in critical condition. The controller of the Centre for Health Protection, Dr Leung Ting-hung, said the Hong Kong man arrived at Tuen Mun Hospital in a taxi via the Shenzhen Bay border crossing on Tuesday. He required treatment for diabetes and minor heart failure and did not develop a fever and other flu symptoms until yesterday. He was then transferred to Princess Margaret Hospital. Health chiefs said it was unclear if the man had any contact with birds or live poultry or in which Shenzhen district he lived. Three relatives who brought him to Hong Kong had returned to Shenzhen and officials there had been contacted to trace them for monitoring, Leung said. Officials are also trying to trace the taxi driver who took him to hospital on Tuesday. Leung said he believed both cases were imported, despite there having been no confirmed H7N9 cases in Shenzhen. He added: "We don't know whether he came into contact with live poultry in Shenzhen, but in Hong Kong, certainly not." Health officials said the chances of the man's relatives contracting the disease were low because he was not coughing, sneezing or suffering from diarrhoea when he was admitted. Leung said it was also unlikely that there was human-to-human spread of the virus. Sporadic cases were to be expected as temperatures dropped, he added. Border checks were stepped up after the first case and three people who stayed in the same ward as the helper - but who showed no symptoms - remain in isolation at the Lady MacLehose Holiday Village in Sai Kung.