Leaves of marijuana are seen at a field near Hlukhiv, Ukraine, Aug 29, 2018. [Photo/Agencies]

The smuggling of new types of illicit drugs, in particular marijuana tar, has increased significantly in the first half of this year, according to Tianjin Customs.

"The administration has cracked 27 cases of illicit drugs and 18 are related to tar from marijuana, accounting for 70 percent of the cases. The numbers of this new type of drug smuggling are on the rise," said Sun Xudong, director of the anti-smuggling bureau of Tianjin Customs.

The bureau has arrested 32 suspects and confiscated 48.8 milliliters of marijuana tar so far this year.

Zheng Xiaoyang, vice-director of the anti-smuggling bureau, said the marijuana tar is similar to the liquid used in e-cigarettes. It is inhaled in a similar way that e-cigarettes deliver liquid nicotine from a chamber.

"The tar is high in concentration and is easy to get people addicted to," said Zheng. He added that just one milliliter could last some users up to six weeks.

Sun said the smuggling and sale of marijuana tar is growing on WeChat and other social media networks. The transactions are completed online and the tar is often disguised in e-cigarette kits. "The criminals mail the tar hidden in other items, in particular in the liquid containers for e-cigarettes and bearing fake names."

He said in recent years, Canada and some US states have legalized the use of marijuana for recreational and medical purposes, which has contributed to the growth in smuggling cases.

The illicit drugs seized recently mostly came from North America. Biscuits and candies containing marijuana were also found by customs.

Li Ming, director of Binhai Airport Customs in Tianjin, said his office has strengthened its efforts to examine imported goods with advanced technologies.

In February, Customs found marijuana tar hidden in 13 packets of egg rolls. Following the discovery, police made arrests in Qingdao, Shenzhen, Chengdu and Shenyang.