I started smoking aged six and was on cocaine at seven

While most children find toys, TV games or ice cream irresistible, Ah Shing, now 15, used to prefer a different indulgence - puffing cocaine, which he has been doing since he was seven.

'I was in Primary Two at the time,' Ah Shing recalls. 'One day, I was brought by my school mates to one of the public housing estates in Kam Tin to meet some young men who then passed the cocaine to me to try ... I had been smoking since I was six. So puffing cocaine was not very exciting to me.

'I did not really like the cocaine at first. But after taking it a few times, I started to enjoy the feeling ... Then I took a bit once every week.'

Ah Shing spent all his pocket money, several hundred dollars a month, buying cocaine from drug dealers in Yuen Long.

Two years ago, he also started using ketamine, sometimes in combination with cocaine. 'Mixing the two drugs was exciting, they make you feel high,' he says.

Ah Shing used to live with his farmer parents and three older sisters in Kam Tin.