THIS is the incredible moment a hero doctor saves an air passenger's life by sucking urine from his bladder non-stop for 37 minutes mid-flight.

Footage from on board a China Southern Airlines plane to New York shows Zhang Hong spring to action to help the stricken 70-year-old.

Incredible footage shows a hero doc removing nearly a liter of urine from an ailing passenger's bladder using his mouth Credit: AsiaWire

Dr Zhang Hong rushed to help the 70-year-old as his bladder got close to rupturing during a mid-air emergency Credit: AsiaWire

Dr Zhang rushed to aid the man after he collapsed in agony and told cabin crew that he was unable to urinate.

A makeshift catheter failed to relieve the ailing passenger's blocked waterworks - leaving little time before his bladder would fatally rupture.

Vascular surgeon Dr Zhang and his colleague Dr Xiao Zhangxiang decided the only course of action was to remove the urine manually.

Dr Zhang used the improvised catheter - made using a plastic tube, syringe and a milk straw - and spent nearly 40 minutes sucking almost a liter of liquid waste from the man's bladder with his mouth.

'DOCTOR'S INSTINCT'

The selfless doc said after his life-saving heroics: "Saving lives is a doctor's instinct."

Cabin crew had issued a desperate plea for any doctors to come forward during the nine-hour flight from Guangzhou this week.

Doctors Zhang and Xiao stepped up to find the elderly man in intense pain with a bloated stomach.

RISK TO LIFE

Dr Zhang later told Chinese media: "He could not sit still and was sweating a lot.

"He was going into shock and may have suffered a risk to his life if we didn't tend to him urgently.

"His family said he had a history of prostate enlargement, so we suspected this was causing urinary retention."

Footage taken in the plane's galley shows the medic repeatedly spitting urine into the empty wine bottle during the life-saving procedure.

Dr Zhang added: "There was no other way. I didn't think too much about it.

"I only wanted to help him extract the urine retained in his bladder.

Dr Zhang Hong used an improvised catheter made from a plastic tube, syringe and a milk straw to perform the procedure Credit: AsiaWire

Dr Zhang Hong, third from left, discusses how to help the ailing passenger Credit: AsiaWire

The hero doc said he was acting on instinct when he came up with the plan Credit: AsiaWire