Four people in New York City's Harlem neighbourhood have died from an outbreak of Legionnaires' disease, an aggressive and potentially deadly form of pneumonia.

The city has seen 99 confirmed cases with 17 people in hospital with the infection, according to the New York City Department of Health.

Officials have traced the outbreak back to 12 cooling towers on 10 buildings where bacteria was growing, including at a hospital and a health clinic.

Eleven of the 12 cooling towers have undergone remediation efforts, and the final one is expected to be fixed on Friday, according to New York Mayor Eric Adams.

Legionnaires' disease is relatively rare, with less than 18,000 people hospitalised in the US every year, according to medical research centre Cleveland Clinic.