Cyclist critical after he was allegedly stabbed while stopping to help a young woman in Portland

A man is in a critical but stable condition after he was allegedly attacked on a Victorian street after stopping to help a young woman.

The 70-year-old man was riding his bike in Portland in the state's south-west last night when the woman flagged him down and asked to borrow his mobile phone.

He was then allegedly stabbed in the upper body before his attacker fled.

He staggered to a nearby home to raise the alarm and paramedics were called to the scene.

A 21-year-old woman has been charged with intentionally causing serious injury and has been remanded in custody to appear in Warrnambool Magistrates' Court on Tuesday.

The man has since been flown to the Alfred Hospital and remains in a critical but stable condition.

Hospital employees said he is doing well considering his age and the amount of blood he lost.

Police told 9NEWS the man was lucky to be alive.