A 19-year-old man has been left with serious injuries after he was stabbed in the neck and chest while on the train near Epping Railway Station on Thursday night, police say.

Emergency services were called to the station at about 11pm after reports that the man, who was travelling from Newcastle to Central, had been stabbed while on the train.

The man was treated at the scene for what police said were "non life-threatening" stab wounds, before being taken to Royal North Shore Hospital in a serious but stable condition.

A spokeswoman for the hospital said that his condition had improved and he was stable on Friday morning.

Officers from Ryde Police Area Command are speaking with witnesses to the incident and will be reviewing CCTV footage to identify the alleged attacker, who left the train at Epping Station.

A police spokeswoman said that while it seems the victim and the alleged attacker were unknown to each other, officers need to speak with the 19-year-old to confirm the circumstances surrounding the incident.

Police are urging anyone with information or who witnessed the incident to come forward.