A man is on the run after stabbing a Sydney CBD bar worker in the back last night.

A group of five men became involved in an argument with staff when they were told to smoke in the designated smoking area.

Police say a 19-year-old man pulled out a knife and stabbed the 34-year-old Concourse Bar worker in the back twice.

The employee has been treated for multiple stab wounds and taken to hospital in a serious but stable condition.

Three men were arrested a short time later and two were charged with multiple offences including assault and affray.

A third man, from Western Australia, has been fined for offensive language.

Detective Inspector David El-Badawi told Ben Fordham they uncovered the 19-year-old was known to them after he left his ID behind.

“I’ve got several detectives and resources out now looking for him.

“If he’s listening, I ask that he hand himself in but we will be catching up to him very soon.”

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Image: Getty