Since last week, Yishun minimart owner Toh Eng Lee has been selling cigarettes kept behind closed cupboard doors.

These were installed ahead of new rules on displaying cigarettes for sale that kick in tomorrow.

But Mr Toh has since seen a 5 per cent drop in cigarette sales.

"Some older customers do not know the brand names and they used to just come and point at the cigarettes," he said. "Now, they are going to other minimarts nearby that have not hidden their cigarettes yet."

Many provision shop and minimart staff worry that the ban will affect sales. However, some retailers said the impact could be mitigated by regular customers.

In March last year, Parliament passed amendments to the Tobacco (Control of Advertisements and Sale) Act, which requires general retailers to keep all tobacco products out of sight of customers.

These rules do not apply to specialist tobacco sellers, who merely have to make sure that their products are not visible from outside the shop.

When The Straits Times visited 15 neighbourhood minimarts and provision shops in Ang Mo Kio, Balestier, Bedok, Clementi, Toa Payoh and Yishun, most had already stored cigarette packets in cupboards or behind curtains and roller blinds. Many shop staff said these had been paid for by the tobacco distributors.

The Straits Times understands that the Tobacco Association (Singapore), which represents the three biggest tobacco companies here, has traditionally provided cigarette cabinets to smaller retailers.

It has therefore been paying for the new cabinets that hide cigarettes from display.

"Now, customers walk in and don't even bother to ask (if we have cigarettes), they just walk out," said Mr Ng Chen Hai, who runs a store in Toa Payoh. He installed the new cabinets about two months ago, and estimated that they have reduced business by 30 per cent.

Some coffee shop owners have also said it is now more troublesome to retrieve the cigarettes, said Mr Hong Poh Hin, chairman of the Foochow Coffee Restaurant and Bar Merchants Association, which represents more than 400 coffee shops, over 90 per cent of which have already made changes ahead of the new rules.

Even then, some retailers are optimistic that their regular customers will continue to stop by for their cigarette fix.

Mr Chen Wen Zhang, who runs An Hua Holdings Minimart in Toa Payoh, said: "Most of our customers are regulars... who already know what we have and what they want."

Said Ms Em Ong, 22, a university student who is a smoker: "I usually buy my pack from the same shops near my school anyway, so I will just go in and ask for the same thing."

• Additional reporting by Cheow Sue-Ann, Sean Lim and Tristan Jeyaretnam