Police have condemned what they have described as the unprovoked stabbing of a police officer at Sydney's Central railway station.
A NSW police officer has undergone surgery after he was stabbed in the back at Sydney's Central railway station.
A 53-year-old man approached Police Transport Command officers about 6.45pm on Friday and stabbed the 30-year-old constable in the back, police said in a statement.
The officer was taken to Royal Prince Alfred Hospital where he underwent surgery overnight and is now in a stable condition.
"He hasn't had a lot of sleep and he is in quite a lot of pain, but I think he is lucky given the circumstances, and is now recovering," Assistant Commissioner Karen Webb said.
The alleged attacker was arrested and taken to St Vincent's Hospital where he remains under police guard while being treated for a cut to his head.
A Sydney Trains employee who witnessed part of the incident said the alleged attacker was tasered by police.
"I just saw this Caucasian guy wielding a knife and the cops were trying to pacify him but he wouldn't stop," the man told ABC TV on Friday.
"He didn't stop so he was tasered."
The matter does not appear to be terror related.
Inquiries into the incident are continuing.
Chief inspector Paul Carrett said a 45 centimetre-long hunting knife was used to stab the officer.
"The bottom line is that policing is a dangerous game and the officer in this case has been very lucky and we are very thankful that he didn't receive more serious injuries," he said.
He said the incident is a reminder of the dangers officers face.
"The stabbing of a police officer unprovoked is a very serious matter, and something that obviously that is concerning to us all the time."