GUANGZHOU - Soon, more than 300 sniffer dogs will stand guard along the Chinese border, ready to rootle out whatever drugs smugglers seek to sneak into the country.

Fifty will be sent to south China's Guangdong Province for a campaign against drug smuggling lasting a month, said Guang Xiangying, head of drug enforcement with the General Administration of Customs.

The dogs can examine tourists, mail and cargo, said Guan.

The dogs' keen sense of smell combined with high-tech devices and tipoffs are expected to find more drugs and deter smugglers, said Yu Jianhuan, an instructor at a dog training base in Shenzhen.

Chinese customs currently has 180 sniffer dogs, most of which are Labradors or golden retrievers with a moderate temperament. Normally a qualified sniffer dog is screened out of 40 dogs.

"Sniffer dogs are more efficient and accurate in checking luggage than the X-ray machines and people," said Yu. The dogs can check a 300-passenger plane in half an hour.

Sniffer dogs have helped Chinese police in nearly 500 cases since 2010 involving drugs, including heroin, cocaine and phenylacetone, a chemical used to produce drugs, more than a fifth of drug smuggling cases since 2010, said Guan.

China's training and use of sniffer dogs by customs has gained international recognition. A memorandum of understanding signed with the World Customs Organization (WCO) in June 2012 turned dog training bases in Beijing and Ruili, Yunnan Province, into WCO Asia-Pacific dog training centers, he said.

Although many drug smugglers receive death sentences, drug use has ballooned in China, with estimates of the real number of drug users somewhere around 14 million.

According to the Office for the China National Narcotics Control Commission, the number of registered drug users in China stood at 2.96 million at the end of 2014, 75 percent of of which were aged under 35.

"The methods of smuggling and concealing drugs evolve all the time and they are hard to detect by machine or by human hand," said Wang Zhanyi, one of only two female sniffer dog instructors in China.

"Sniffer dogs can find hidden drugs faster and better," she said, "and that's what we are striving for."