A man has been brutally savaged by a herd of cows in south Auckland, tearing out chunks of flesh and leaving him with gaping wounds.

A witness to the attack, Mike Small, told NZME he was cycling through Totara Park on Sunday afternoon with his wife when he heard a blood-curdling scream.

He saw a woman was on the ground being brutally attacked by several cows. Suddenly a man dashed in to help her.

"All of a sudden this guy appeared and helped her to her feet and then the cows knocked him to the ground and trampled him," Mr Small says.

"There were front feet off the ground raining down on him. They were head down and if they had horns they would have been goring him."

The attack left the victim "smashed up" and suffering horrific injuries.

"He had a laceration about the size of a palm out of the back of his hamstring, just ripped off... and another couple of tennis ball sized chunks out of his shin," Mr Small told NZME.

"There's no nice way to put it: He got f**ked up."

The original victim called St John to send an ambulance and paramedics arrived minutes later.

Ms Small says they had to carry the victim away from the enraged animals so his injuries could be attended to.

A St John spokeswoman told NZME they attended the incident and a patient with moderate injuries was taken to Middlemore Hospital.

Newshub.