A vape disguised as a highlighter in a child's pencil case is one of the many reasons the federal health minister is pushing for an e-cigarette crackdown.

Mark Butler said vapes were being being "shamelessly marketed to kids".

"A parent told us only over the last week they discovered in their very young child's pencil case a vape that was disguised as a highlighter pen," Mr Butler told ABC radio on Wednesday.

Mr Butler has flat out refused legalising access to nicotine vapes following a push by the Nationals and lobby groups earlier this week, saying it is a "terrible idea".

"It's not normalised, it's a black market which has been allowed to get out of control," he said.

"There was not the cynical level of marketing even of cigarettes that we see in these vapes.

"Vapes that have pink unicorns on them, that are bubble gum flavoured."

Under Australian laws, it is illegal to buy, possess or use nicotine for vaping without a doctor's prescription. Only pharmacies can sell e-cigarettes or e-liquids that contain nicotine.

Vapes sold on black markets have resulted in more children - even those in primary school - taking up vaping, Mr Butler said.

The Nationals want the laws changed to allow retailers to dispense nicotine vaping products but limit sales to people 18 and over, similar to tobacco regulations.

A new study by the Australian National University found that most use of e-cigarettes is not for smoking cessation.

Most smokers who vape continue to smoke and most use in young people isn't about quitting smoking, the report said.

More than 240 chemicals were found in toxicological analyses of non-nicotine e-cigarettes.

At least 38 of those chemicals were listed poisons and another 27 were associated with adverse health outcomes.

Users of nicotine e-cigarettes could also be poisoned by the nicotine itself, the study said.

Nicotine poisoning can cause seizures and respiratory depression, which can result in death, according to Cancer Council Victoria.

The ANU study was published in the Medical Journal of Australia.