NSW Health has seized more than $3 million of the banned products since July 2020.

Chief Health Officer Kerry Chant said retailers were being put on notice, if they were selling the contraband.

"We are cracking down on the illegal sale of nicotine e-cigarettes and liquids and taking a zero-tolerance approach to those who sell them," she said.

"You will be caught, illegal items will be seized, and you could face prosecution, resulting in being fined or even jailed," Dr Chant said.

"People think they are simply flavoured water but in reality, in many cases they are ingesting poisonous chemicals that can cause life threatening injuries," Dr Chant said.

The curb on illegal nicotine sales extends to online shops with the maximum penalty $1650 per offence, six-months in prison or both.

Selling to minors also comes with hefty fines of up $55,000.

The Alcohol and Drug Foundation says around 14 per cent of 12 to 17-year-olds nationwide have tried an e-cigarette, with around 32 per cent of these students having used one in the past month

Around 12 per cent of students reported buying an e-cigarette themselves.

Australian Associated Press