A 30-year-old police officer stabbed in the back with a hunting knife at Sydney's Central Station last night is in a stable condition after undergoing surgery.

Key points: The 30-year-old police officer suffered a stab wound to his back and was taken to hospital in a stable condition

The 30-year-old police officer suffered a stab wound to his back and was taken to hospital in a stable condition A man was arrested at the scene and carried out by other officers

A man was arrested at the scene and carried out by other officers Witnesses said the arrested man was seen yelling at officers before the incident

Constable Hayden Edwards from the police transport command section of NSW Police was taken to hospital after being attacked on one of the station's platforms about 7:00pm on Friday.

Speaking on Saturday morning, NSW Police said a 53-year-old man had been arrested.

Police said the officer was slashed across the back with a "45cm hunting knife" in an "unprovoked attack".

The knife police allege was used in the attack ( Supplied )

"It was [a] rather large [knife]," NSW Police Assistant Commissioner Karen Webb said.

"Having seen the knife, our officer is very lucky to have walked away with only minor injuries.

"He was dealing with an unrelated matter."

Constable Edwards has been with the NSW Police for three years.

A witness said there was blood on the ground beside a man who was seen being carried out by half a dozen officers, and there was pepper spray in the air.

A NSW Ambulance spokesman said three crews attended.

"We treated a 30-year-old man for a single stab wound to his back," he told the ABC.

"He's stable and has been taken to Royal Prince Alfred [Hospital]."

Witnesses said the arrested man was seen wielding a knife. ( ABC News )

A Sydney Trains employee who witnessed part of the incident said the arrested man was shot with a Taser.

"I just saw this Caucasian guy wielding a knife and the cops were trying to pacify him but he wouldn't stop," the man, who declined to give his name, told the ABC.

"He was shouting at the cops and then he didn't stop so he was tasered. A cop went down to platform one and grabbed the knife."

The employee said the officers handled the situation "professionally".