Man charged over Sydney officer's stabbing

A 53-year-old man has been charged after a NSW Police officer was stabbed in the back with a hunting knife at Sydney's Central railway station on Good Friday.

Transport officers were dealing with an unrelated matter on a platform when the man allegedly approached Constable Hayden Edwards and stabbed him from behind about 6.45pm.

The 30-year-old officer was taken to Royal Prince Alfred Hospital where he underwent surgery for a six centimetre cut to his back overnight.

Const Edwards was discharged from the hospital on Saturday evening.

The alleged offender used a 45cm-long hunting knife which had a 30cm blade, Assistant Commissioner Karen Webb said.

"Having seen an image of that knife - our officer is very lucky to only have minor injuries," Ms Webb told reporters on Saturday.

"(It) was an unprovoked attack. We allege the offender has approached with some vigour."

The alleged attacker was arrested after being stunned with a Taser and taken to St Vincent's Hospital where he was treated for a cut to his head.

He was released from hospital on Saturday morning and taken to Sydney Police Station.

The 53-year-old was charged with wounding with intent to cause grievous bodily harm, using an offensive weapon to prevent lawful arrest, resisting arrest and having a knife in a public place.

He's due to face Parramatta Bail Court on Sunday morning.

Const Edwards, who has been with the police force for three years, only recently moved to Sydney after transferring from Moree in northern NSW.

Chief Inspector Paul Carrett said the "very competent" officer was sore and tired after the attack.

"A stabbing of a police officer - unprovoked - is a very serious matter," Insp Carrett.

The police union described the attack as "cowardly" and said it highlighted the dangers police officers face on the job.

"The offender has just walked up behind the police officer, who was doing his job talking to someone else, and stabbed him in the back," Police Association of NSW president Tony King told reporters on Saturday.

"It's a cowardly act from behind."

A Sydney Trains employee witnessed part of the incident.

"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 attack didn't appear to be terror-related, NSW Police have said.

© AAP 2019