Chinese authorities say they’ve busted a crime ring that used a system of drones, cables and motorized pulleys to sneak nearly $80 million worth of smartphones from Hong Kong to Shenzhen, in what is said to be the country’s first known cross-border smuggling operation involving drones.

In Shenzhen, a major technology hub sometimes referred to as China’s Silicon Valley, authorities arrested 26 people and seized two drones and thousands of iPhones, state media and Reuters reported. In Hong Kong, customs officers arrested three people and seized 900 smartphones, according to the Hong Kong-based South China Morning Post. The joint sting operation was conducted in February but the details weren’t released until Friday.

“It’s the first case found in China that drones were being used in cross-border smuggling crimes,” the state-owned Legal Daily reported.

Authorities said the suspects are members of several gangs who worked under the cover of darkness to move huge volumes of undeclared, refurbished iPhones and other devices across the border.

One group would set up in a pair of high-rise condos in Shenzhen and use drones to fly cables over a border fence to another group on the roof of a village house about 660 feet away in Hong Kong, according to state media. The cables were then attached to motorized wheels, in what authorities called a “flying line.”

Once the system was in place, authorities said, the smugglers clipped bags filled with smartphones to the cables and pulled them across the border.

The scale of the alleged operation is staggering. Authorities said bag after bag carrying about 20 devices could be whizzed across the border in seconds. The suspects typically worked from midnight to 5 a.m. about 15 days per month, transporting 10,000 to 15,000 smartphones each night, according to customs officials quoted in the South China Morning Post. They estimated the suspects took in 10 million yuan (about $1.6 million) monthly.

The suspects also allegedly took steps to conceal their activities, installing soundproofing materials that dulled the noise of the pulley system, according to the South China Morning Post.

Investigators said a tip from a member of the public led them to the buildings on either side of the border, according to Legal Daily. All told, the suspects smuggled 500 million yuan (about $79.5 million) worth of devices, officials said.

After announcing the arrests, officials held a news conference in which they demonstrated how the “flying line” worked.

Cracking down on the use of civilian drones has been a heavy lift for China, the world’s largest drone manufacturer. Last year, the government issued new regulations requiring most commercial drones to be registered under owners’ real names, following incidents in which the flying robots disrupted air traffic.

Although drone-assisted smuggling on the Shenzhen-Hong Kong border appears to be new, the use of zip lines for surreptitious transport isn’t. According to the South China Morning Post, customs officials in 2011 broke up a smuggling ring that used fishing line — apparently shot over the border with a crossbow — to ferry gadgets into Shenzhen.

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