Mystery bashing at chicken farm leaves man fighting for life

A man is fighting for life after being assaulted at a chicken farm in Adelaide's north.

The 59-year-old was found with critical head injuries at the Hillier Road property in Hillier after another man, 24, phoned police this afternoon.

There was "quite a bit of blood" at the scene, a police spokeswoman said.

The injured man was taken to the Royal Adelaide Hospital in a critical condition.

Mystery surrounds the circumstances of what happened and when.

The 24-year-old is assisting police as major crime detectives investigate, but it is believed he is not a suspect in the attack.

The bashing left locals on edge.

"They keep a low profile and just go about their farming thing," one neighbour said.

"It's just a pretty ordinary farm really."

Anyone with information is urged to contact Crime Stoppers on 1800 333 000.