'Even possession of one tablet is an offence,' said Mr Tong, referring to his branch's resolve to prosecute people found with even trace amounts of illegal drugs. Mr Tong said the biggest difficulty was trying to stop individuals bringing Ecstasy and other psychotropic drugs into Hong Kong.

Heroin is still the most prevalent drug seized in terms of weight, with 33kg in the past seven months, followed by methamphetamines, including 'ice' (25kg) and cannabis (12kg).

But from January to July, 65,086 tablets of psychotropic drugs were seized, along with 29,114 tablets of Ecstasy. That total of 94,200 tablets is roughly twice the total of 49,493 last year for both Ecstasy and other mood-altering substances.

The number of people under 21 arrested for drug-trafficking offences has increased, with 56 arrests in the first seven months of this year compared with the total of 65 for last year.

Part of the reason for the increase in cross-border cases was price, Mr Tong said. The cost of imported Ecstasy tablets can be more than $300, while mainland-made tablets cost between $80 and $140.

Drugs with hypnotic effects - including estazolam and midazolam - cost a fraction of their Hong Kong price on the mainland. A tablet of estazolam, a common tranquiliser, cost about $30 in Hong Kong but less than $1 in Shenzhen, he said.

More body searches will be carried out at checkpoints to deter people from bringing in the drugs and Mr Tong's branch has begun trading information with authorities on the mainland and in Thailand. 'We will work with this intelligence to stop drugs coming into Hong Kong,' he said. 'We will also add inspectors to the [land] borders in October.'

Another anti-drug measure to be implemented at Lowu, Lok Ma Chau, Chek Lap Kok and other border control points was the expanded use of 'passive-alert' sniffer dogs, Mr Tong said.

Trained to sit quietly and only point their noses at the sources of drug odours, these labradors will not tip off traffickers until it is too late.

By the end of January, the narcotics dog unit will be expanded to include 31 officers, 20 normal drug-detecting dogs and six passive-alert animals. The unit now has 21 officers, 13 drug-sniffing dogs and two passive-alert animals.

The Customs and Excise Department also plans to further mechanise its land-border crossing booths in the next two years by installing 42 video cameras to automatically record vehicle registration numbers.

This automatic vehicle recognition system will cut the number of human errors and reduce waiting times at Hong Kong's three land crossings.