A charity is providing a water-based therapy to help ease the condition. Nora Zheng reports from Hong Kong. 

Two young men with autism, frightened and confused, stood beside a swimming pool, ready for their first scuba diving lesson. Suddenly, the older youth screamed, began punching himself in the head and dropped to the ground, rolling around in an uncontrolled fit.

That scene, from the summer of 2016, is etched in the memory of Chan Leung-bo, 52, former deputy chairman of the Hong Kong Underwater Association.

A nearby parent called out anxiously, "Is he a simpleton? Is he dangerous? Will he hurt my child?" The parent could hardly be blamed for being concerned, as the distressed youth was 1.8 meters tall and weighed 90 kilograms.

On the other side of the pool, a coach working with a group of children kept blowing his whistle, exhorting his students to "Go!" to keep them focused on their training.

People with autism have problems with social interaction and verbal and nonverbal communication to varying degrees, depending on the severity of their condition.

It was hoped that the diving class at the Guangzhou Polytechnic of Sports in Guangdong province would help to ease the autistic episodes of the two youths, ages 18 and 20.

Two coaches had been recruited to help, but the noise, the unfamiliar surroundings and the crowded pool proved unsettling. Chan turned to the stricken youth's mother, who stood weeping nearby. "Do you want to give up?" he asked. "If you want to continue, I'll be with you."

The mother said "Yes". She wanted every effort made to help her son.