Border patrol officers inspect a hole on Tuesday. The hole was dug by smugglers in a garage to use as an underground passage linking Shenzhen, Guangdong province, and Hong Kong. Xue Yunhui / For China Daily

New ways of smuggling goods to Guangdong province from neighboring Hong Kong — including underground passages and sky ropes — have become more common, a border patrol officer said on Wednesday.

Goods smuggled from Hong Kong are mostly electronic products, which are less expensive than similar items on the mainland, said Mo Shu, inspection head of the sixth branch of the Frontier Defense Corps of Guangdong province.

"This year we found that smugglers really like to use underground passages and sky ropes to smuggle such goods," Mo said.

Mo said that in the past, smugglers usually used trucks and ships. But sources with the provincial border patrol authority said it had uncovered four cases this year in which smugglers moved goods through underground passages.

The goods included more than 500 smartphones, 140 Apple iPads and more than 400 hard drives.

In a separate case, smugglers used underground culverts to illegally move ivory into Shenzhen, which borders Hong Kong, the authority said.

"In such cases, smugglers loaded goods on boats in Hong Kong, then transported goods through designated underground culverts to Shenzhen," Mo said.

In the most recent case, border patrol soldiers in Shenzhen discovered and sealed an unfinished tunnel under a residential complex garage on Dec 19. Authorities believe the tunnel would have been used to smuggle goods from Hong Kong, sources with the Guangdong Frontier Defense Corps said.

The unfinished tunnel, which had an opening in Ganglianyi village in Shenzhen, was about 40 meters long, 80 cm wide and 1 meter tall, Mo said.

Inside the tunnel, border patrol officers found lights, ventilation pipes, carts, track, ropes and pulleys.

Police seized the equipment and arrested an owner of the garage.

"But no smugglers have been arrested. The case is still under investigation," Mo said.

The property owner told police the garage was rented in August to a man who was later found to have used a fake identification card.

"The tunnel was intended to be used to smuggle cellphones, hard drives, tablet computers and other electronic products from Hong Kong to Guangdong to evade customs duties and other taxes," Mo told China Daily.

The illegal shipment of goods is also well above ground, as well as under it.

Smugglers often use pulleys and ropes connecting high buildings in Hong Kong and Shenzhen, Mo said.

"Buildings between Hong Kong and Shenzhen are as close as 30 meters. Smugglers can easily put ropes and pulleys on such buildings," Mo said.

Such smuggling usually can be accomplished within five minutes, Mo said.

Last December, border patrol officers uncovered a smuggling case in which smugglers transported more than 200 smartphones from Hong Kong to Shenzhen via ropes and pulleys.

Mo said authorities in Guangdong and Hong Kong have been cracking down on such smuggling cases.

By the end of November, border patrol authorities in Guangdong had uncovered 504 smuggling cases this year in which goods were transported from Hong Kong and Macao.