China Southern Airlines has warned passengers not to drink alcohol before flying.

The airline had to treat three in-flight passengers who had been drinking before boarding flights between May 12 and May 15.

On May 12, a passenger surnamed Wu was calling for help from flight attendants, waving his hands around on a flight from Zhengzhou, capital city of Henan Province, to Shenzhen.

"Come on, I can see nothing," he cried. When flight attendants reached him, they smelled strong alcohol and found him in a cold sweat and short of breath. They laid him down, covered him with a blanket, gave him oxygen and traditional Chinese medical massage.

Wu regained consciousness and normal breathing 10 minutes later while an ambulance was called to meet the flight at the Shenzhen airport.

The next day, another passenger who had taken alcohol before boarding felt short of breath, with blurred vision and a headache during the flight. A doctor on board treated him.

The third passenger on a flight between Shenzhen and Chongqing took down a life-jacket and inflated it. Flight attendants had to restrain him. After he sobered up, he apologized and offered to compensate the airline for any damage.

The air pressure inside the cabin when a plane was flying could have some negative impact on an intoxicated passenger, the airline warned.

Editor: Donald