Health authorities are scouring the Sydney Town Hall area to find the source of a legionnaires' disease outbreak.
Four men are being treated in hospital for the disease after spending time in the CBD area bounded by Clarence, Pitt, Park and King streets, Dr Vicky Sheppeard from NSW Health told the ABC on Thursday.
Tens of thousands of commuters pass through the area each day and it's also a focal point for tourists.
Cooling towers in the area are being inspected as outbreaks are often associated with contaminated air-conditioning systems in large buildings.
Dr Sheppeard said 20 samples from cooling towers had been taken for testing and the remaining towers would be sampled on Thursday.
Field teams were also looking at other water sources in that part of the city, including fountains.
Legionnaires' disease is a type of pneumonia caused by a bacterial infection of the lungs that can develop after someone breathes contaminated water vapour or dust.
Australian Medical Association president Brian Owler said he understood the outbreak occurred in the five days to March 3, and it was coming towards the end of the incubation period.
Legionnaires' could be fatal in people who were already very sick, and most cases could be treated with antibiotics.
"If you do have those symptoms of a respiratory illness, fever, sweats, cough ... see your GP, but particularly if you were in that area, around the Sydney Town Hall," he said.
NSW Health is also urging anyone who has visited the Town Hall area and has symptoms such as fever, chills, a cough and shortness of breath to see their doctor.
