A GROUP of four people have been hospitalised after inhaling a chlorine-type gas at the Great Artesian Spa complex in Mitchell.

A Queensland Fire and Rescue Service spokesman said officers were called to the Cambridge St complex at 5.19pm yesterday.

"It appears the individuals received exposure to two different chemicals," the spokesman said.

He said the chemicals produced a chlorine gas effect.

Chlorine gas is known to produce acid when it reacts with water in the respiratory system.

A Queensland Ambulance Service spokeswoman said they were all taken to Mitchell Hospital with inhalation injuries before three were flown by the Royal Flying Doctor Service to Toowoomba Hospital for further treatment.

A Toowoomba Hospital spokeswoman this morning confirmed two women patients had been discharged last night but one man remained in hospital.