CENTENARIAN mainlander Yang Meijun is paying a seven-day visit to the territory to teach people the secret of a long-lasting and healthy life - the ancient taoist art of da yan qi gong. Despite smoking 20 cigarettes a day, at 100 and still spry, Ms Yang says she is living testimony to the efficacy of qi gong, which involves breathing exercises modelled on the movement of wild geese. Ms Yang is the 27th in a line of students of the art which stretches back 1,700 years. She said she owed her long life to the benefits of practising qi gong for almost 80 years. ''I started the exercise when I was 13. It involves harmonising and adjusting the yin and yang. It can cure all types of disease,'' Ms Yang said. In China, Ms Yang made her living curing the ill using her special knowledge and teaching it - against tradition - to more than one pupil. One of her students, Peter Wong Wing-keung, said Ms Yang was right to have broken this rule of the taoist art. ''It was stated through the years that da yan qi gong should be taught to only one student and when the teacher is over the age of 70, but Ms Yang has taught many of us,'' he said. There are 300 followers of the art in Hong Kong. Ms Yang said smoking helped her to breathe out ''sick air'' that she ''absorbed'' from her patients when healing. ''I never use drugs to heal people. I take the air of sickness out from the patients and absorb it into my body. That's why I have to smoke so often. I breathe out the bad air together with the smoke,'' Ms Yang said. She said her health was not harmed by smoking because the nicotine of the cigarettes was excreted through the skin when she exercised. Ms Yang gave a free seminar and demonstration of qi gong yesterday evening at the Southorn Playground Stadium in Wan Chai. She returns to her Beijing home on Monday.