A US farmer who was moments away from being sucked into a machine has revealed the life-saving decision to cut off his trapped leg with a pocket knife.

Nebraska grain grower Kurt Kaser said he had “no other choice” but to use a knife to self-amputate the lower half of his left leg after getting stuck in a grain auger – a piece of farm equipment that uses a rotating screw blade.

The 63-year-old was using the auger to transfer grain into a bin and forgot that part of the screen covering the moving parts was missing.

As he got out of his truck, Mr Kaser accidentally stepped on the grain auger opening, which resembles a large drill bit.

“It grabbed ahold of me,” he told US broadcaster ABC.

“I can remember seeing it start and I go, ‘This ain’t good,’” Mr Kaser added.

“And then when my foot was in there banging around, I was trying to hold my leg, pulling it out, and I said, ‘This is not good’”.

A grain auger sucked Mr Kaser’s leg in. Photo: Getty

There was no one else on his farm to call for help and Mr Kaser did not have his phone on him when the accident happened on April 19.

Unsure how long he would be able to remain conscious, he remembered he was carrying a 7.6cm blade and made the split-second decision to saw off his own leg about eight inches below his knee.

“I had my pocket knife in my pocket. I said, ‘the only way I’m getting out of here is to cut it off,’ so I just started sawing at it,” he told KETV.

Mr Kaser said he felt a slight “ping” as he cut through the nerve endings but overall didn’t experience much pain or notice a lot of blood.

“Adrenaline kicked in so much that I don’t know if it hurt or not,” he said.

He then managed to “army crawl” about 45 metres “on rock and gravel” to get to the nearest phone.

Kurt Kaser is thankful to be alive after the accident. Photo: Madonna Rehabilitation Hospitals

After calling the ambulance, Mr Kaser was rushed to the nearest hospital, where he spent weeks undergoing rehabilitation before returning home on May 10.

“I never lost consciousness until they … started operating on me.”

Once his leg heals, Ms Kaser will be fitted with a prosthetic limb.

He has spent three weeks undergoing rehabilitation, during which he has noticed other patients who were in much worse shape than him.

“I mean, they’re in wheelchairs. They’re not getting out of them. It could always be worse,” he said. “I get a chance to be pretty close to normal. They don’t and I feel sorry for them.”