Seven-hour surgery after Vic rider slashed

Victoria Police are looking for witnesses to a horrific knife attack that left a woman with injuries so severe the 34-year-old required seven hours of emergency surgery.

The woman was riding home via North Melbourne when she was stopped by two men and a woman about 2.30am on Wednesday.

One of the men slashed her chest, arms, neck and face with a box cutter before the trio fled with her mobile phone.

Deputy Commissioner Shane Paton on Thursday said detectives were seeking witnesses and also gathering any available CCTV footage to identify the attackers.

"She was in surgery for six or seven hours yesterday because of this absolutely horrific, unprovoked attack," Mr Paton told 3AW.

"After the attack (she) managed to ride on for a period of 50 to 100 metres to flag down some help."

The woman, who is likely to be scarred for life, remains in a stable condition in the Royal Melbourne Hospital.