Three people have been admitted to hospital with Legionnaires’ disease in Sydney, prompting warnings for others to monitor for symptoms.

The South Eastern Sydney local health district is advising anyone who has been in the Sydney CBD and Clarence Street area since December 9 to be aware of signs of the severe respiratory illness.

The warning comes as three people, unknown to each other, developed Legionnaires’ disease after spending time near those areas between December 9-18.

The source of the outbreak was not yet confirmed and it was possible the cases were not linked, the local health district’s acting director of the public health unit Professor Mark Ferson said on Sunday.

Symptoms can develop up to 10 days after exposure and include fever, chills, a cough and shortness of breath and can lead to severe chest infections such as pneumonia, Ferson said.

“Those most at risk include elderly people, people with underlying lung or other serious health conditions, and smokers,” he said.

Outbreaks of Legionnaires’ disease sometimes occur when bacteria from environmental sources including soil or cooling towers atop large buildings become contaminated.

NSW Health said it was working closely with the City of Sydney to test cooling towers in the area.

Legionnaires’ disease is caused by infection with Legionella bacteria.

It is not spread from person to person.

-AAP