People who have been in central Sydney are being warned to watch out for symptoms of Legionnaires' disease with seven cases were recorded in the past three weeks.

Three women and four men, aged from their 20s to 70s, visited locations in the CBD on separate occasions in the 10 days before developing symptoms.

All seven people have been admitted to hospital for treatment of pneumonia, NSW Health said on Wednesday.

Legionnaires' symptoms can include fever, chills, a cough and shortness of breath, which can lead to severe chest infections such as pneumonia. The disease cannot be spread from person to person.

The Legionella bacteria that causes the disease is often associated with contaminated cooling towers of large buildings.

People can be exposed to the bacteria if contaminated water particles from a cooling system are emitted into the air and breathed in.

Those most at risk are people with underlying lung or other serious health conditions and people who smoke.

NSW Health environmental health officers are working with the City of Sydney Council to inspect cooling towers.

Review of maintenance records of cooling towers in the CBD area will also help determine further towers to be inspected and sampled.

Managers of buildings with cooling towers are being contacted and informed of the cluster.