The deadly H7N9 bird flu virus has arrived in Hong Kong, it was confirmed last night. The city activated its flu contingency plan after an Indonesian domestic worker who recently travelled to Shenzhen was found to have contracted the deadly new strain, the first case in the city. The 36-year-old patient is in a critical condition in Queen Mary Hospital, Pok Fu Lam, with severe pneumonia and breathing with the help of an artificial lung. The live-in helper works for a couple with two children, and all four were said to have minor flu symptoms and were under observation in quarantine at Princess Margaret Hospital. Secretary of the Food and Health Bureau Dr Ko Wing-man said: "Since the helper had travelled to Shenzhen, where she had killed and cooked a live chicken, we believe it is a case imported [from the mainland]." Health officials are looking for a second person who accompanied the helper to Shenzhen on November 17. The helper developed flu symptoms four days later. She was first treated at Tuen Mun Hospital, but was transferred to Queen Mary last Wednesday. Ko said two earlier tests for the virus came back negative, but a third test last night confirmed she had contracted H7N9. He added that the risk of human-to-human transmission could not be ascertained yet, but he activated the city's three-level response system set up to deal with a potential flu pandemic. It was set at the "serious level", one step below the top emergency level. Live poultry imports from three Shenzhen farms will be suspended until the Centre for Health Protection completes an investigation. Since the first case of H7N9 infection in a human was reported in February, the virus has killed 45 people, all on the mainland. About 138 people on the mainland were infected and one in Taiwan. Most of the cases were in Zhejiang and Jiangsu provinces and Shanghai. In November, a three-year-old boy in Dongguan , Guangdong, was confirmed with the disease. University of Hong Kong microbiologist Ho Pak-leung said there was not enough evidence to show that the virus could spread between humans. Ho said the public should remain vigilant, but there was no need to panic.