Shenzhen's border police have reported an increase in the number of people caught trying to illegally enter Hong Kong so far this year by hiding underneath lorries.

The city's exit and entry frontier inspection authorities said 34 people were caught since January, almost double the total number last year, according to a China Daily report earlier this week.

However the authorities attributed the rise to their improved surveillance work, saying it was a result of their increased action against this new means of human trafficking. The phenomenon has been curbed, with only four people caught since the beginning of May.

Most of the people caught secretly snuck under lorries that were transporting goods between Shenzhen and Hong Kong while drivers were away or the vehicle was stationary, and hid in some basic shelves beneath the chassis, the Daily said.

There have also been several instances of people hiding underneath trains.

The authorities launched a special campaign in January to improve checks under lorries. Efforts were also made to remind drivers to carefully check their vehicles before leaving for Hong Kong.

Drivers are fined between 6,000 (US$750) to 10,000 yuan if anyone is found underneath their lorry.

The total number of offenders dropped since the mainlanders in a few cities, including Shenzhen, were allowed to pay individual tours to Hong Kong since 2004. However, there are still people taking the risk.

Many of them try to enter Hong Kong to work illegally, while others use the city as a way to leave for foreign countries, the report said.

Editor: Yan