LONDON (Reuters) - One in three of all the young men in China will eventually be killed by tobacco unless a substantial proportion of them succeed in quitting smoking, researchers said on Friday.

"Without rapid, committed, and widespread action to reduce smoking levels, China will face enormous numbers of premature deaths," said Liming Li, a professor at the Academy of Medical Sciences in Beijing who co-led a large analysis of the issue.

The study, published in The Lancet medical journal, found that two-thirds of young men in China start to smoke, mostly before age 20, and that unless they quit for good, around half of those who start will eventually die from their habit.

The scientists conducted two large, nationally representative studies 15 years apart, tracking the health consequences of smoking in China. The first was in the 1990s and involved a quarter of a million men. The second study is ongoing, and involved half a million men and women.

The results showed annual number of tobacco deaths in China, mostly among men, had reached a million by 2010. If current trends continue it will be 2 million by 2030.

Among Chinese women, however, smoking rates have plummeted and the risk of premature death from tobacco is low and falling, the study found.

The researchers said the consequences are now starting to emerge of a large increase in cigarette smoking by young men in recent decades. The proportion of all male deaths at age 40 to 79 attributed to smoking has doubled to around 20 percent now from about 10 percent in the early 1990s. And in urban areas this proportion is higher, at 25 percent and rising.

Smoking causes lung cancer, which is often fatal, and is the world's biggest cause of premature death from chronic conditions like heart disease, stroke and high blood pressure.

Richard Peto a professor at Britain's University of Oxford who co-led the research, said price hikes on cigarettes in China may be one way to reduce smoking rates.

"Over the past 20 years tobacco deaths have been decreasing in Western countries, partly because of price increases. For China, a substantial increase in cigarette prices could save tens of millions of lives."

(Reporting by Kate Kelland; Editing by Toby Chopra)