When a half-tonne bull started mauling an elderly farmer like a "savage dog", truckie Marcus Thompson launched himself at the enraged beast.

Mr Thompson, 39, a Woodville stock driver, punched and kicked the aberdeen angus-cross last week after it turned on its owner, Upper Hutt man John Leitner.

The attack left Mr Leitner, who will be 80 tomorrow, with serious injuries to his head and chest, including a punctured lung and several broken ribs. He remains in intensive care in Wellington Hospital.

"The bull just nailed him from behind; it just dropped him straight to the ground and jumped on him basically," Mr Thompson said yesterday.

"It was down on its front knees mauling him with its head – thank God it didn't have horns."

The pair had been loading nine bulls on the truck on Mr Leitner's Masterton farm last Thursday to take to a Taranaki works.

While Mr Leitner lay prone, Mr Thompson and another man rushed to help.

"We were into it, hitting and kicking it, just trying to distract it to get it off him," he said.

Eventually the pair managed to get the beast into a paddock, and Mr Thompson phoned for help.

"The bull was a mental case by then, it kept coming back over to us and trying to get to us," he said.

"It smashed through two or three fences, just went straight over them basically."

The bull then charged into two arriving police cars, clipped an ambulance, then stoved in the side of Mr Leitner's car.

A police officer shot and killed the animal.

Mr Thompson, a father of two with 20 years' trucking experience, said he did not think twice before helping.

"People have patted me on the back and said 'Well done', but there was no way I could stand there and watch ... My wife is pretty proud of me, though."

Mr Leitner's wife, Wendy, said yesterday he was still in intensive care and needed a ventilator to help him breathe.

He had suffered five or six shattered ribs, a punctured lung and other "crush injuries" to his chest and sides, but was likely to make a full recovery.

"He's absolutely maroon and blue, with bruises everywhere," she said.

Mr Leitner, also known as Hans, was born in Austria and moved to Wellington in 1958. He fractured his skull and damaged his spine while mountain climbing in Austria, his wife said.

"He's tough as guts, although he's been in and out of hospital so often I think he's trying to get permanent residency there.

"I don't know what I'm going to do with that man of mine."