A homeless woman has stabbed a man near a busy intersection in Melbourne's CBD, police say.

The 29-year-old man was stabbed on Elizabeth Street, near the intersection of Collins Street, about 4.15pm on Wednesday.

The man and woman were reportedly involved in an altercation, before the man was stabbed in the stomach.

A 55-year-old woman was arrested at the scene, near an Officeworks store and Subway fast food outlet.