There, these products are subject to heavy taxes and can be sold at high prices on the black market. Because of busy traffic at the border checkpoints, they are seldom checked.

Mainland customs officials recently tightened border inspections but smugglers have been able to stay one step ahead by making more trips across the border, each time carrying only a few high-value items which they say are for self-use and as such are exempt from duty.

Guangdong customs officials say all travellers entering or leaving mainland customs checkpoints more than once a day must go through special channels. They would face more thorough inspections and any item valued at more than 5,000 yuan (HK$6,133) would only be given tax exemption on their first trip, the Southern Metropolis News reported yesterday. Duty payable on the mainland ranges between 10 and 50 per cent.

The measures cover seven checkpoints: Lowu, Huanggang, Shenzhen Bay and Shatoujiao in Shenzhen and Gongbei, Hengqin and Wanzhai in Zhuhai. Shenzhen's Futian checkpoint will not be included, for reasons which were not specified.

The measure is expected to have an impact on Hong Kong shops, particularly those in the New Territories.

Lau Oi-kwok, chairman of the General Chamber of Pharmacy, said businesses in Hong Kong, particularly pharmacies close to the border in areas such as Sheung Shui, may see trade drop by 20 per cent as a result of the policy. 'It will be quite a blow to pharmacies in those places if the rule is to be strictly implemented,' he said. 'Business at those pharmacies will be reduced by as much as 20 per cent, I think, because quite a lot of parallel [import] traders buy products like milk powder from them.'

From Sunday, the General Administration of Customs will impose a new tariff on travellers bringing merchandise worth more than 5,000 yuan into the mainland, with luxury goods such as cosmetics and wine to be taxed at 50 per cent.

Analysts said the new measures were intended to boost domestic consumption by cracking down on 'ant smuggling' gangs and overseas shopping agents after products worth an estimated 40 billion yuan were taken into the mainland without tax being paid on them at a time of high inflation and high domestic-consumption taxes.

In 2010, more than 1,000 smugglers were seized by Shenzhen and Zhuhai customs officials in a month-long crackdown on the smuggling of electronic and luxury products from Hong Kong and Macau to the mainland without the payment of taxes. Mainland authorities also introduced a blacklist system, with officers automatically alerted when 'ant smugglers' crossed the border to Shenzhen.

Additional reporting by Adrian Wan

1,000

More than this number of smugglers were seized by Shenzhen and Zhuhai customs officials in a month-long crackdown in 2010