A man in India had to have his penis partially amputated after he developed gangrene from an erection that lasted two days, international media report.

The unnamed 52-year-old presented himself to doctors because he couldn't get rid of the 'painful and sustained' erection, a case report published in the British Medical Journal says.

Bungling medics swiftly drained the blood from his penis, but left a catheter in and tightly dressed his penis, causing the patient to develop black gangrene.

They were left with little option but to amputate after he reported back to them showing signs of severe tissue damage caused by an acute loss of blood circulation.

Details of the highly-unusual case, which occurred at King George's Medical University in Lucknow, northern India, were published last month in the British Medical Journal.

The man had been suffering from priapism, a medical term for a persistent and painful erection.

It is not known what caused the patient's condition but experts consider an erection lasting more than 48 hours a medical emergency.

The NHS says priapism can be caused by sickle cell disease or by the use of illegal or legal prescription drugs for erectile dysfunction, including Viagra.

"We removed his urethral catheter," Dr Saqib Mehdi wrote in the case report.

"But still the black colour of glans penis deepened over the next day and a clear line of demarcation became visible between it and the penile shaft."

Three weeks after the life-changing operation the man was able to urinate as usual and now has a 'healthy wound.'