Hong Kong confirmed Tuesday a new human case of the deadly H7N9 avian flu found in an 18-month-old girl, the sixth case to be discovered in the city.

Fears over avian flu have grown following the deaths of three men from the H7N9 strain in Hong Kong since December last year, all of whom had recently returned from mainland China.

The child, who had also recently visited the mainland, was hospitalised on February 28 after developing a fever and was treated in an isolation ward, the city's health department said in a statement.

She was sent home "in a stable condition" on Monday but routine laboratory test results later showed positive for the virus, the statement said.

The girl is now in isolation in another hospital undergoing tests, but has no fever or symptoms.

She had travelled to the neighbouring Chinese province of Guangdong for three weeks in February, the health department said, where her mother had taken her to a wet market -- though they did not buy poultry.

Family members and patients from the first hospital that admitted the child will be taken in for testing and observation, the statement said.

Others who may have had contact with the girl will be "put under medical surveillance", it added.

A total of 31 people died from H7N9 bird flu in mainland China in January, the government said, making it by far the worst month of the outbreak. There were a total of 127 confirmed human H7N9 cases that month, according to the National Health and Family Planning Commission.

The outbreak, which first emerged on the mainland in February 2013, has reignited fears that a bird flu virus could mutate to become easily transmissible between people, threatening to trigger a pandemic.

Hong Kong slaughtered 20,000 chickens in January after the virus was found in poultry imported from Guangdong.

Officials said last month that they were extending for four months a ban on live poultry imports from mainland China to guard against the disease.

Hong Kong is particularly 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.