Nearly 30 percent of the over 1,900 teenagers surveyed in Hawaii were found to have tried e-cigarettes, and of those, 17 percent were using e-cigarettes only. The overall rate is about three times higher than previously reported in the US studies in 2011 and 2012, which showed rates of 4.7 percent and 10 percent respectively, the researchers said.

"You have to think carefully about the risks and benefits of using either tobacco or nicotine, which is known to be an addictive substance," said Thomas Wills from University of Hawaii Cancer Center."A lot of teens think it is easy to quit smoking but it isn't true. It's hard for anybody to quit," Wills added.

He said e-cigarettes are widely available in the absence of restrictions on their sale, and that may help explain why the rate of use is so high in Hawaii. The study appeared in the journal Paediatrics.

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