The nation's top doctor has advised Australians who feel ill after returning from Bali to seek treatment after an outbreak of Legionnaires' disease on the popular Indonesian resort island.

Commonwealth chief medical officer Jim Bishop said Australian health authorities knew of 11 cases of Legionnaires' disease detected in Victorians and Western Australians after holidays in the Kuta area of Bali between August 2010 and January 2011.

Anyone who has flu-like symptoms such as fever and cough following a trip to the region should visit their GP or take themselves to a hospital emergency department, he added.

“There are specific antibiotics available to treat the disease,” Professor Bishop said on Wednesday.

“The time between a person's exposure to the bacteria and becoming sick is usually between two to 10 days.”

Indonesian health authorities and the World Health Organisation are investigating the outbreak.

Professor Bishop said they were testing water samples from possible sources of the disease and had told hotels in the area to disinfect and clean their water supply systems.

A number of people who caught Legionnaires' had stayed in the same hotel in Kuta – the Ramayana Resort and Spa – and most had visited the same local shopping centre.

Legionnaires' disease is contracted by breathing in very fine droplets of water which contain the bacteria.

People most at risk of are those aged over 50, smokers, and anyone whose immune system is suppressed by medication or diseases such as cancer, kidney failure or diabetes.