A Canadian visitor is in hospital with a fractured skull, bleeding on the brain and spinal injuries after an alleged group assault in Byron Bay late last night.

Police say the 28-year-old man flagged down a patrol car on Butler Street about 11.40pm after escaping from a group that had allegedly attacked him.

Officers provided first aid before taking him to Byron Bay Hospital.

He was later transferred to Tweed Valley Hospital, where he remains in a serious but stable condition.

Police allege the man had been drinking with about five males he did not know in a park on Jonson Street shortly before the incident.

Investigators believe he was assaulted by members of the group before fleeing through nearby bushland and eventually attracting the attention of passing police.

The man suffered a fractured skull, bleeding on the brain and spinal injuries.

Detectives have commenced an investigation and are appealing for witnesses to come forward.

Police believe two of the males involved may be aged about 16 or 17.

Anyone who was in the area at the time, or who has dashcam or mobile phone footage that may assist investigators, is urged to contact Byron Bay Police or Crime Stoppers on 1800 333 000.