Photos of rabbits in Colorado with black, horn-like growths around their faces have gone viral, with some describing the animals as "Frankenstein-", "zombie-" and "demon-rabbits".

Colorado Parks and Wildlife officials have identified the cause as shope papillomavirus, a rabbit-only virus with no cure that produces wart-like tumours known as papillomas, particularly around the face and head of cottontail rabbits, 9NEWS reports.