A senior official with the country's top tobacco watchdog has expressed doubts over the credibility of a study which suggests that some Chinese cigarettes contain too many heavy metals, saying simply comparing Chinese and Canadian cigarettes is not scientific.

A study released on Thursday by the International Tobacco Control Project shows that some Chinese cigarettes have significantly high levels of heavy metals, with some containing about three times the level of lead, cadmium and arsenic of Canadian cigarette brands.

The brands involved include Honghe, Hongtashan and Baisha, and the metal content in tobacco comes from the contaminated soil in which the tobacco leaf is grown, the study shows.

However, Wang Xiansheng, deputy director of the technology department of China's State Tobacco Monopoly Administration, expressed doubts over the study's credibility.

"I don't think the research which simply compares Chinese- and Canadian-made cigarettes can be trusted and so far there are no standards on tobacco products' heavy mental concentration in China and the world," he said on Saturday.

Wang made no direct comments on the heavy metal content level in Chinese-made cigarettes.

An unnamed official with the general office of the Shanghai Tobacco (Group) Co told the Yangtze Evening News on Saturday that the high heavy metal concentration detected in the cigarettes comes mainly from tobacco leaves.

"It's related to many factors including the natural environment where they grow, so that's not under the control of the tobacco producer," the officer was quoted as saying.

Official documents show the heavy metal problem has caught the attention of the administration.

A document posted by the administration's website in 2009 says tobacco plants are prone to absorbing heavy metals from the soil they grow in and the heavy metal inhaled by people while smoking could harm their health.

"To work out technologies addressing the problem will help improve consumers' health and the competitiveness of Chinese-made tobacco products in the global market," the document says.

Experts warn that almost all of the heavy metals have known health effects: arsenic is a poison, cadmium can cause cancer and lead is toxic to the brain - and these metals get into smokers' bodies along with a cocktail of other toxins.

"The presence of such contaminants in an already deadly consumer product demonstrates the need for strong regulation of tobacco products. Smokers and non-smokers in China and elsewhere deserve to know what is in their cigarettes," said Richard O'Connor with the Roswell Park Cancer Institute, New York, who led the study.

Each year, 1 million smokers die from tobacco-related diseases in China, and another 100,000 die from exposure to secondhand smoke. If current trends continue, China's death toll from tobacco will reach 2 million a year by 2020, official statistics showed.

Worse, knowledge about the harm of cigarettes is far lower in China than internationally, the new study shows. Only 68 percent of smokers in China believe that smoking leads to lung cancer and only 36 percent believe smoking causes heart disease.

In addition, more than 70 percent of Chinese smokers wrongly believe that "light" or "low tar" cigarettes are less harmful, a previous survey showed.

"Weak cigarette package warnings are ineffective at educating the public about the serious consequences of smoking," said Wang Ke'an, director of the Think Tank Research Center for Health Development, a non-governmental organization based in Beijing.

The warnings on the back of cigarette packages in China are written in English and fewer than 10 percent of smokers in China understand them, he said.

A survey of 1,200 people across four Chinese cities found the warning labels to be much less effective than warning labels from other countries, especially those with graphic images.