MIAMI (AFP) - Almost seven in 10 US school kids are exposed to e-cigarette ads which promote the battery-powered vaping devices using themes of rebellion, sex and independence, US health authorities said Tuesday (Jan 5).

Unrestricted marketing of e-cigarettes has been accompanied by a dramatic increase in the number of vaping youths, raising concerns about health dangers and a new generation of people addicted to nicotine, The US Centers for Disease Control and Prevention said.

From 2011 to 2014, current e-cigarette use among high school students went from 1.5 per cent to 13.4 per cent, the CDC said.

Among middle school students, users went from 0.6 percent to 3.9 percent in the same time span.

In 2014, e-cigarettes became more commonly used among youth than any other tobacco product, including cigarettes.

"The same advertising tactics the tobacco industry used years ago to get kids addicted to nicotine are now being used to entice a new generation of young people to use e-cigarettes," said CDC director Tom Frieden.

"I hope all can agree that kids should not use e-cigarettes."

More than 18 million middle and high school students see e-cigarette ads, according to the CDC Vital Signs report.

The data came from the 2014 National Youth Tobacco Survey, which showed that 68.9 per cent of middle and high school students "see e-cigarettes ads from one or more media sources." More than half (55 per cent) saw ads in retail stores, while 40 per cent saw them online and 37 percent saw them on TV or in movies.

Thirty per cent of youths said they saw the ads in newspapers and magazines.

E-cigarettes deliver nicotine by heating a flavored liquid that is inhaled by the user.

Research has shown that nicotine exposure "at a young age may cause lasting harm to brain development, promote addiction, and lead to sustained tobacco use," the CDC said.

The report also said that spending on e-cigarette advertising rose from US$6.4 million (S$9.1 million) in 2011 to about US$115 million in 2014.