Hong Kong on Saturday quarantined an additional 19 people after the city confirmed its second human case of the deadly H7N9 bird flu, less than five days after it confirmed its first, officials said.

The 19 people were close contacts of the second carrier of H7N9 in the city -- an 80-year-old Hong Kong man who had been living in the neighbouring mainland Chinese city of Shenzhen.

The man developed a fever and was found to be infected with the virus on Friday after he was admitted to the city's Tuen Mun hospital on Tuesday due to underlying medical conditions.

"Nineteen close contacts of the patient have been quarantined," a government statement released late Saturday said.

Out of the 19 quarantined, 13 had stayed in the same cubicle with the elderly man at the city's Tuen Mun hospital, five were his family members, and one other was the taxi driver who drove him from the border to the hospital, the statement said.

Eighteen of the quarantined patients have tested negative for the deadly virus, while the test results for an "asymptomatic" patient was pending. All 19 will be quarantined for 10 days since their last contact with the carrier.

Officials are still investigating whether or not the 80-year-old patient, who remains in stable condition, had come into contact with poultry on the mainland.

On Monday the city admitted a 36-year-old Indonesian domestic helper who was infected with the virus.

"She has a history of travelling to Shenzhen, buying a chicken, slaughtering and eating the chicken," Hong Kong health minister Ko Wing-man had said of the patient, who remains in a critical condition.

Health officials said they have not found any links between the two cases.

The government has placed 17 people who had been in close contact with the Indonesian patient under quarantine since Tuesday.

Hong Kong is especially alert to the spread of viruses after an outbreak of Severe Acute Respiratory Syndrome (SARS) swept through the city in 2003, killing 299 people and infecting around 1,800.

In all, 138 human cases of H7N9 have been reported in mainland China since February with 45 deaths, according to the World Health Organization.