Two of the state's most reviled killers, Adrian Ernest Bayley and Steven James Hunter, have exchanged blows in Victoria's maximum-security Barwon Prison.

The pair is understood to have broken out into a fight on Friday last week, briefly landing Hunter in hospital.

Adrian Bayley is behind bars for the rape and murder of Jill Meagher.

It's believed the 53-year-old – who is behind the stabbing murders of two young women – was treated for a minor head injury but was returned to his prison cell near Geelong the same day.

Bayley, 47, was treated for minor injuries.