Objective This study aims to understand the age patterns of smoking initiation during adolescence and young adulthood in South-West China, where the prevalence of tobacco use is reported as the highest in the country.

Design A cross-sectional study.

Setting The data were derived from the China National Nutrition and Health Survey in Yunnan Province, South-West China (2010–2012).

Participants A total of 4801 participants aged 15–65 years were included.

Primary outcome measures A survival model was used to estimate the hazard of smoking initiation by age and log-rank test was used to compare the hazard curves across subgroups (men/women, urban/rural, Han Chinese/ethnic minority).

Results The prevalence of current smoking among men and women were 60.4% (95% CI 58.2% to 62.6%) and 5.1% (95% CI 4.3% to 5.9%), respectively. Smoking was more prevalent among men and women of lower education and less income, as well as rural and ethnic minority women. Among the current smokers, cigarette (80.7%) was the most commonly used tobacco product, followed by waterpipe (10.8%) and pipe tobacco (8.5%). The hazards of smoking initiation were low for both men and women before the age of 15 years (1% for men and 0.05% for women); and the hazards increased quickly from age 15 years and peaked at 19years (21.5% for men and 1.0% for women). Rural and ethnic minority women were at higher risk of smoking initiation than their counterparts between 15 years and 19 years of age (χ²=44.8, p<0.01; χ²=165.2, p<0.01) and no such difference was found in men.

Conclusions Findings of this study underscore the importance to implement tobacco prevention interventions among older teens and young adults in South-West China, especially for rural and ethnic minority women.