The changes have been triggered by a Financial Action Task Force meeting at the weekend, which introduced measures targeting cross-border cash movements.

Hong Kong has opted for a so-called disclosure system, rather than mandatory currency declarations as seen in the United States and Canada.

Under the new system, Hong Kong customs officials can stop and question passengers about the money they are bringing into Hong Kong and must keep a record of individuals carrying more than US$15,000, even if it is not related to a crime.

'People are not obliged to declare the money on crossing the border,' Commissioner for Narcotics Rosanna Ure Lui Hang-sai said. 'But if asked to [by customs officials], they do [have to disclose the cash], and a record will be kept.'

The taskforce has said this must be executed either on a targeted basis, based on intelligence or suspicion, or at random. Hong Kong will have to show compliance by providing statistics, and will be monitored on site by taskforce officials.

The measures had been discussed with the Customs and Excise Department, which said it could take on the extra role without adversely affecting passenger flow, Mrs Ure said.

Legal amendments will need to be introduced to widen the ambit of money-laundering seizure powers, which Mrs Ure said would likely cover 'serious crimes'. At present, the law focuses on the proceeds of drug trafficking.

The taskforce measures have come under fire, however, for being misguided and unrealistic in a jurisdiction such as Hong Kong, which has a fluid flow of cash coming across the border, from the mainland in particular, on a daily basis.

'In terms of addressing terrorism financing, I couldn't think of a more useless thing to do if you tried,' said Peter Gallo, director of risk management firm Pacific Risk. 'It's creating bureaucracy for bureaucracy's sake.

'If it will have an effect at all, it will be on the capital flow out of China, but certainly not terrorism.'

Hong Kong's retail, property and tourism sector has been flush with cash from the mainland following a relaxation on travel restrictions.

Anecdotal evidence suggests the mainland's capital controls are being flouted with relish, a phenomenon that may be adversely affected by the new measures.

According to Hong Kong Monetary Authority figures, 7.17 billion in yuan deposits was being held by Hong Kong bank customers in July. In February, the central government allowed banks to introduce yuan services that would give a limited avenue for the cash.

Mrs Ure said other means of spending yuan, such as credit cards, were gaining ground in Hong Kong.

'The likelihood of them [mainland tourists] taking a lot of money just for a day trip is quite small,' she said. 'US$15,000 is a generous ceiling.'