The Health Sciences Authority (HSA) said it confiscated 5,356 of the devices, known as e-cigarettes or "vapers", last year, almost three times the seizures in 2012.

This compared with only 10 such seizures in 2009.

The battery-powered devices deliver a puff of nicotine vapour in a variety of possible flavours, minus many of the toxic chemicals present in a cigarette.

HSA said there was no conclusive scientific evidence to show that e-cigarettes help smokers quit tobacco use.

It added that health authorities are "concerned that e-cigarettes could potentially be a gateway to developing a smoking habit".

The agency says it watches websites and forums to monitor the illegal trade of e-cigarettes inside Singapore.

It said eight people have been prosecuted since 2011 for selling them.

Their import, distribution or sale is punishable by fines of up to Sg$10,000 ($7,951).

Singapore is one of the costliest cities to buy conventional cigarettes, with a pack of Marlboros costing around Sg$13 ($10.30).