A suspected gas leak has left one person dead and six others in hospital, including five police officers who responded to to an emergency call from a restaurant.

Emergency services were called to to Haveli Indian Restaurant on Garfield Street in Riverstone , in Sydney's north west suburbs, at 9.15am on September 16.

Fire and Rescue NSW Superintendent Adam Dewberry said a person was found non-responsive inside the building, and they were unable to be revived, after the restaurant reported a suspected gas leak to police.

"All we know is that the air quality in the whole building, two levels, has been compromised," Superintendent Dewberry said.

"It was obvious to the first arriving emergency services that the air quality in the building was compromised," he said.

"Hazardous materials e

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