Hong Kong officials said Wednesday the discovery of a bacteria that cause Legionnaires' disease at the new government complex was "under control", while it was probing the source of the deadly bug.

In a major embarrassment to the city's government, ten water samples taken from various places at the harbourfront complex have been tested positive for Legionella, which causes Legionnaires' disease, a severe form of pneumonia.

The findings came after the city's education minister was hospitalised for nearly two weeks due to the potentially fatal disease. The bacteria found in a tap in his office washroom was about 14 times over the acceptable amount.

The bug was also found at the offices of the chief executive Donald Tsang and several ministers, as well as at the canteen and a bakery, according to health authorities Tuesday, prompting a major disinfection exercise.

"Overall the situation is under control," health chief York Chow told a news conference, saying the water tanks and more than 1,000 water outlets inside the complex have been cleaned and disinfected.

After the news conference, health authorities disclosed that a tenth water sample, taken from the home minister's office before the disinfection work, also tested positive for Legionella.

Authorities said earlier that water samples taken from the main water tanks have tested negative for Legionella, allaying fears of a possible outbreak.

Critics blamed that a rush to move into the buildings, launched last August, has compromised the sanitisation work, saying the bacteria are normally found in old buildings.

But the top health official dismissed the claims.

"There is no evidence to show the moving in schedule of our bureaus into this building is the cause of this particular discovery," said Chow.

"We have only one patient so far, and the discovery of this bacteria has yet to be concluded," said Chow, adding that health authorities need more time to investigate how the bacteria got into the buildings.

Legionnaires' disease is caused by bacteria that grow in water, particularly warm environments such as hot tubs, hot water tanks, plumbing systems and air-conditioning systems.

It is contracted through inhalation of contaminated water droplets and is not known to be transmitted from person to person.

Legionnaires' disease was named after an outbreak occurring in a Legion Convention in the United States in 1976.