Workers place partially assembled electronic cigarettes in a tray Feb. 19 at the Ruyan factory in Tianjin, China.The battery-powered products, which resemble real cigarettes but produce a fine nicotine spray absorbed quickly and directly by the lungs, are gaining ground in America, Europe and China, which is home to 350 million smokers.

Beijing ? With its slim white body and glowing amber tip, it can easily pass as a regular cigarette. It even emits what look like curlicues of white smoke.

The Ruyan V8, which produces a nicotine-infused mist absorbed directly into the lungs, is just one of a rapidly growing array of electronic cigarettes attracting attention in China, the U.S. and elsewhere — and the scrutiny of world health officials.

Marketed as a healthier alternative to smoking and a potential way to kick the habit, the smokeless smokes have been distributed in swag bags at the British film awards and hawked at an international trade show.

Because no burning is involved, makers say there’s no hazardous cocktail of cancer-causing chemicals and gases like those produced by a regular cigarette. There’s no secondhand smoke, so they can be used in places where cigarettes are banned, the makers say.

Health authorities are questioning those claims.

The World Health Organization issued a statement in September warning there was no evidence to back up contentions that e-cigarettes are a safe substitute for smoking or a way to help smokers quit.

It also said companies should stop marketing them that way, especially since the product may undermine smoking prevention efforts because they look like the real thing and may lure nonsmokers, including children.

“There is not sufficient evidence that (they) are safe products for human consumption,” Timothy O’Leary, a communications officer at the WHO’s Tobacco Free Initiative in Geneva, said this week.

The laundry list of WHO’s concerns includes the lack of conclusive studies and information about e-cigarette contents and their long-term health effects, he said.

Unlike other nicotine-replacement therapies such as patches for slow delivery through the skin, gum or candy for absorption in the mouth, or inhalers and nasal sprays, e-cigarettes have not gone through rigorous testing, O’Leary said.

Nicotine is highly addictive and causes the release of the “feel good” chemical dopamine when it goes to the brain. It also increases heart rate and blood pressure and restricts blood to the heart muscle.

Ruyan — which means “like smoking” — introduced the world’s first electronic cigarette in 2004. It has patented its ultrasonic atomizing technology, in which nicotine is dissolved in a cartridge containing propylene glycol, the liquid that is vaporized in smoke machines in nightclubs or theaters and is commonly used as a solvent in food.

When a person takes a drag on the battery-powered cigarette, the solution is pumped through the atomizer and comes out as an ultrafine spray that resembles smoke.

Hong Kong-based Ruyan contends the technology has been illegally copied by Chinese and foreign companies and is embroiled in several lawsuits. It’s also battling questions about the safety of its products.

Most sales take place over the Internet, where hundreds of retailers tout their products. Their easy availability, O’Leary warns, “has elevated this to a pressing issue given its unknown safety and efficacy.”

Prices range from about $60 to $240. Kits include battery chargers and cartridges that range in flavors (from fruit to menthol) and nicotine levels (from zero — basically a flavored mist — to 16 milligrams, higher than a regular cigarette.) The National Institutes of Health says regular cigarettes contain about 10 milligrams of nicotine.

On its Web site, Gamucci, a London-based manufacturer, features a woman displaying one of its e-cigs. “They look like, feel like and taste like traditional tobacco, yet they aren’t,” the blurb reads. “They are a truly healthier and satisfying alternative. Join the revolution today!”

Smoking Everywhere, a Florida-based company, proclaims it “a much better way to smoke!” while a clip on YouTube features an employee of the NJoy brand promoting its e-cigarettes at CES, the international consumer technology trade show.

Online sales make it even more difficult to regulate the industry, which still falls in a gray area in many countries.

In the U.S., the Food and Drug Administration has “detained and refused” several brands of electronic cigarettes because they were considered unapproved new drugs and could not be legally marketed in the country, said press officer Christopher Kelly.