Following a huge increase in reports of under-age e-cigarettes sales, Lancashire County Council trading standards officers, supported by the police, carried out test purchasing operations during half-term.
Volunteers aged between 14 and 16 visited 29 shops and were able to buy disposable vape pens from 11 of them.
The illegal sales occurred in the Chorley, Leyland, Rawtenstall, Fleetwood, Cleveleys, Lancaster, Morecambe, Preston, and Kirkham areas. Investigations into the sales are ongoing.
County Councillor Peter Buckley, cabinet member for community and cultural services, said: "These sales are illegal and potentially damaging to young people's health. We won't tolerate anyone selling vaping products to children under the age of 18.
"This test purchasing crackdown is vital to ensure that local businesses are operating within the law. We're very concerned that a third of the shops visited sold vaping products to under-18s.
"A number of shops that were visited during these operations have previously received warning letters and advice in relation to the law in this area, so we need to carry out further investigations as to why the sales were made and take action to ensure it doesn't happen again."
Action trading standards could take includes using its enforcement powers to issue cautions, or prosecute sellers and business owners, which can result in fines of up to £2,500.
County Councillor Michael Green, cabinet member for health and wellbeing, said: "Vaping can be very damaging to young people's health.
"The major issue is young people who do not already smoke taking up vaping. This can lead to them moving on to cigarette smoking, and potentially forming a habit that could be massively damaging to their health. The other concern is the high level of nicotine that can be delivered by vaping devices.
"Most of the products in this test purchasing crackdown cost just £4 - £10, which are pocket money prices for many children.
Further trading standards test purchasing operations will be carried out in the coming months.
Anyone wanting help and support to stop smoking can contact the Lancashire Quit Squad, a free service provided by the NHS and commissioned by the county council.