Paramedics treated 24 patients after a chemical leak at a hotel in Sydney's CBD on Wednesday morning.

Emergency services were called to the Pullman Hotel near Hyde Park just after 9am to reports mixed chemicals had gone into the ventilation system, an ambulance spokesman said.

There were 10 ambulance crews on scene, and six patients who appeared to be asthmatic were taken to St Vincent's Hospital as a precaution.

A NSW Ambulance paramedic said everyone transported to hospital was in "a very stable condition".