Cigarette packages should show graphic images of yellow teeth, blackened gums, protruding neck tumors and bleeding brains to alert smokers to their disease risks, the World Health Organization said on Friday.

More than 20 countries, including Britain, Iran, Peru and Malaysia, already use visual warnings on their tobacco products, the head of the WHO's Tobacco Free Initiative said.

"Although some people question the need for such pictures, the evidence is absolutely clear that they convince people to quit," Douglas Bettcher told a news conference ahead of World No Tobacco Day, to be held on Sunday.

Bettcher pointed to a warning that read "smoking causes brain strokes" and showed blood oozing from a brain.

He has called for such images to be printed on all tobacco product packages and on tags to water pipes that are popular in the Middle East. Bettcher added that the "disgust, fear, sadness or worry" from the warnings can discourage smoking.

The WHO, which requires all its staff to be non-smokers or to agree to try to quit, has been campaigning for more than two decades to discourage smoking and fight efforts by big companies such as Philip Morris International, Imperial Tobacco, Japan Tobacco and British American Tobacco to attract new customers.

Bettcher said the tobacco industry opposed visual warnings, viewing them as a threat to profits.

Tobacco is the world's leading preventable cause of death, killing more than 5 million people a year, the WHO says,

Around 80 percent of smokers live in developing countries, where smoking rates have risen sharply in recent years alongside a ramping-up of tobacco marketing and production in poorer states, Bettcher said.

In addition to package warnings, the WHO supports bans on tobacco marketing and sponsorship, prohibitions of smoking in public buildings, and high taxes on tobacco products.

The recent emergence of designer cigarette pack-holders and other accessories to cover up health warnings showed the warnings were having an impact, Rob Cunningham of the Canadian Cancer Society said.

"That is a good indication, because smokers are noticing enough that they feel that they must not look at them," Cunningham said.