A 25-year-old man is dead and six others, including police officers, are in hospital after a gas leak at a restaurant.

Five officers and another person were taken to hospital on Tuesday morning after going to the site in Sydney's northwest.

NSW Police Assistant Commissioner Gavin Wood said the officers tried to revive the man, administering CPR amid extremely high levels of carbon monoxide.

"It's a tragedy in terms of loss of life," he told reporters.

"Early indications are he (the deceased) may well have been employed within that restaurant environment."

Mr Wood described the officers who were taken to hospital as "extremely brave".

"I want to acknowledge the police who put their lives at risk going into the environment, commencing CPR, trying to save this young man's life and now t

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