Guests of the Pullman Sydney Hyde Park hotel have been treated for respiratory problems and eye irritations after a gas leak.

Key points: Hydrochloric acid and chlorine were mistakenly mixed by a hotel staff member

Hydrochloric acid and chlorine were mistakenly mixed by a hotel staff member The gas spread from the pool area through the ventilation system

The gas spread from the pool area through the ventilation system Six hotel guests have been taken to hospital

NSW Ambulance told the ABC that 30 patients were treated at the scene and eight were taken to hospital.

The patients complained of eye and airway irritation and one person had difficulty breathing, Acting Superintendent Steve Vaughan said.

The fumes were created when a hotel staff member, who was tending to the pool, mistakenly mixed hydrochloric acid and chlorine.

The gas then spread through the ventilation system on the 22nd floor and about 9:00am guests reported an odour.

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"They were naturally emanating from the container and they got into the air-handling system and the lift shafts," said NSW Fire and Rescue duty commander Charles Begley.

"If you're exposed directly to them long term, it can be quite serious for your respiratory system," Mr Begley said.

One guest from Brisbane, who asked to remain anonymous, said there was a chemical smell throughout the hotel.

"Everybody [was] coughing," he said.

"[It] was stinging."

Christina Sticovich, who was with her husband Tillio on holiday from Auckland, said it was a scary ordeal.

"We were a bit shocked and surprised," she said.

Staff initially thought it was nothing and said it was a drill, Ms Sticovich said.

The hotel said it was investigating the matter and working with authorities.