An Indian policeman who spent two months swallowing knives and had 40 of them surgically removed said "spiritual powers" made him do it.

The father of two underwent a successful five-hour operation to remove the knives from his stomach in the northern city of Amritsar, after complaining to doctors of severe abdomen pain.

"I don't know why I did it but there was some spiritual power behind it," the 42-year-old said from Amritsar in Punjab state, declining to be named.

"It started in June when I swallowed the first knife and I enjoyed the feeling. It soon became a habit."

Doctors said they initially thought he was suffering from a tumour after body scans showed a large solid mass.

But on further investigation, they discovered dozens of folding knives with metal and wooden handles, measuring up to 18 centimetres unfolded.

"We immediately prepared him for surgery and removed the knives. There was bleeding as some of them were unfolded," Rajinder Rajan, one of the surgeons at Corporate Hospital, said.

Dr Rajan said he suspected the patient, who told doctors he passed two more knives in his stools, was suffering from depression.

Doctors said they initially thought he was suffering from a tumour after body scans showed a large solid mass. ( AFP/The Corporate Hospital )

Although recovering well from the surgery, he would undergo a psychological assessment before being discharged from the hospital, Dr Rajan said.

Doctors have not ruled out the possibility he had pica disorder, in which the sufferer feels compelled to consume non-edible things.

But the man said he would not do it again.

"I consumed a knife a day for about two months. I never felt it was going to harm me but when it pained, I came to the hospital," he said.

"I will not repeat it. I am glad they saved my life and I want to go back to my family."

AFP