When an elderly plane passenger fell ill mid-flight Tuesday, a courageous doctor with a stomach of steel rose to the occasion.

Dr. Zhang Hong saved the man’s life by spending 37 minutes sucking urine from his blocked bladder with nothing but a plastic tube and an empty wine bottle.

China Southern Airways Flight CZ3009 was far from its takeoff point in Guangzhou, China — and still six hours from its destination, New York — when a man with a bloated stomach began sweating profusely around 1 a.m.

The cabin crew made an emergency announcement, asking if there was a doctor on board. Dr. Hong quickly identified the problem — and its hard-to-stomach solution.

“When I saw that the man could hardly bear the pain anymore, my only thought was how to get the urine out of his bladder,” Hong, head of vascular surgery at Jinan University’s First Affiliated Hospital, told the South China Morning Post.

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

Hong questioned the senior’s on-plane relatives about any past medical issues. “His family said he had a history of prostate enlargement, so we suspected this was causing urinary retention,” Hong told the outlet.

That’s when Hong diagnosed exactly what was happening: The man’s bladder was so bloated with urine, it was at risk of rupture.

China’s the Paper reported Hong shouted, “Fast! Help me get a cup!”

Fellow surgeon Xiao Zhanxiang swiftly helped his colleague MacGyver a catheter out of a piece of plastic tubing, the straw of a milk carton, sticky tape and a syringe from the plane’s medical kit.

Flight attendants spread blankets in the aisle and the doc went to work.

However, when Hong realized the syringe’s needle was too thin, he quickly moved on to the necessary but nasty backup plan: using his mouth to extract the urine.

With consent from the man’s family, Hong spent the next 37 minutes sucking 800 milliliters (about 1½ pints) of urine from the senior, spitting it into a wine bottle as he went.

Chaotic footage taken of Hong working on the man was watched over 20 million times in less than 24 hours.

The brave act saved the man’s life — but the doctor considers his actions merely logical.

“Saving lives is a doctor’s instinct,” he said. “There was no other way. I didn’t think much about it.”