A child is in a serious condition and over a dozen people have been treated after a chemical spill at a western Sydney community pool this morning.

Emergency services were called to the Wollondilly Leisure Centre in Picton about 10.00am (AEDT) after reports of people being affected by chemicals.

NSW Ambulance deputy director of critical operations Ian Johns said they treated 14 people — mostly young children taking swimming lessons — for health issues caused by the spill.

"It turns out some chemicals were mixed with the pool and some people had an adverse event," he said.

One child is in a serious condition and two other children and an adult are in stable conditions at Campbelltown Hospital.

Another adult and child were taken to Bowral Hospital in a stable condition.

"The chemicals gave off a gas and caused minor breathing and airway irritation and some localised skin and eye irritation," Mr Johns said.

"So once they were out of the affected area, paramedics were assessing and treating … thankfully [only] minor irritation this morning."

Loading

A statement from the Wollondilly Shire Council said there was "an operational need to use a super dose of disinfectant".

"Unfortunately a chemical spill occurred during this process, resulting in fumes, and emergency services were called by the contracted operator of the facility," the statement said.

"Emergency services have arranged for the observation of those who have pre-existing respiratory issues."

Wollondilly Shire Council has shut down the facility's indoor pool but the rest of the venue remains open.