SYDNEY, Dec. 3 (Xinhua) -- Nine children, aged under six, have been treated for breathing difficulties by paramedics at a Sydney swimming pool, after an incorrect mixture of chemicals created a noxious gas cloud.

Emergency services were called to the Wollondilly Community Leisure Centre in the city's southwest at around 10:00 a.m. local time on Monday.

Local media reported that chlorine was incorrectly added to a mixture, creating a gas cloud which affected the children leading to them requiring medical treatment.

Health workers ventilated the area and the gas cloud dissipated.

The swimming pool will remain closed until emergency services have cleared the area.