This would criminalise many more producers, who would become punishable by the death penalty China already had in place for drug trafficking.

Fentanyl, which is 50 times stronger than heroin with some more powerful derivatives, has become a staple of drug lords, but represents a nightmare for law enforcement because of highly secretive production, encrypted online transactions and its easy transportation by international mail.

The United States has named China as the main source of the deadly painkiller, which was responsible for 28,466 fatal overdoses in the US last year, according to the US’ Centres for Disease Control and Prevention.

Prosecuting those manufacturing such drugs depends on including them on a “controlled” list, but the legal process of adding a substance to the list can take months.

Beijing already has 27 fentanyl-related substances on its controlled list, going further than the United Nations requires, yet the formula for the synthetic drug can be marginally altered to stay within the law while carrying the same risks of addiction and overdose.

“If China amends its law to specify the core ingredients of fentanyl, it will become harder to avoid prohibition by making a slight variant on the banned version,” said Vanda Felbab-Brown, senior fellow with the Brookings Institute.

“But it will still need to enforce its laws, meaning conducting raids and monitoring of pharma factories to make sure illegal drugs are still not being produced or legal fentanyl for medical purposes being diverted to illegal use.”

As the world’s largest exporter of active pharmaceutical ingredients, China boasts tens of thousands of pharmaceutical and chemical factories, making strict regulation a daunting task.

Criminals are known to evade investigation with tactics including setting up factories in remote areas, producing illegal drugs as a sideline to legal operations, and using non-local staff, past investigations have shown.

According to police in Changde in central China’s Hunan province, who in 2016 busted a legitimate factory that produced hydroxylamine hydrochloride – a raw material for ketamine – said drugs factories were usually found in chemical industrial parks in less developed areas.

Locations would be remote but with easy access to highways, while production would be mixed with legal products and raw materials would be identified by code names.

Such factories would usually bar outsiders from entering and use secretive means to hire staff.

“The task of restricting the production of fentanyl and related substances are formidable,” said Spencer Li, professor with the Faculty of Social Sciences at University of Macau and also President of Asian Association of Substance Abuse Research.

“Anyone with rudimentary skills and basic technological knowledge can set up a factory in an obscure place to make this kind of stuff.”

There is still scope for progress by governments, Li said.

“The Chinese government can control the production and transportation of fentanyl through its elaborate and pervasive network of social control, at least to some extent,” he said.

Even though it is not possible to identify and shut down all drug-producing labs, regular monitoring and crackdowns would help disrupt the networks, as China did for methamphetamine and heroin labs, according to Felbab-Brown.

Zhejiang in eastern China, one of the provinces that is home to numerous chemical plants, has pledged stricter controls on psychoactive drugs after “production, distribution, transportation and trade of such drugs have been spreading in recent years and seriously tarnished the province’s international image”, according to a Zhejiang government document.

Inspections of chemical factories will be held regularly, the document stated, with a focus on those involved in international trade as well as those using a production address different from their business registration address or renting a workshop and equipment for psychoactive substances production.

The document also requested that plant employees help in inspecting sites that are deserted or in remote locations, to prevent them being used by criminals for illegal drugs production.

Along with a crackdown on production, tighter controls of customs and postal services are being called for to reduce exports of fentanyl to the US.

According to a report last year by the US-China Economic and Security Review Commission – a body founded by the US Congress – Chinese chemical manufacturers export fentanyl-related drugs to small-scale drug distributors and criminal organisations across the United States.

The drugs are marketed online, exported with deliberate mislabelling to evade regulations and often mailed through a chain-like forwarding system.

Professor Li said it has become increasingly difficult to control transactions generated by drug trafficking because drugs can be distributed easily through multiple channels and it would take a joint effort by multiple nations, including China and the US, to stop the flow.

Nonetheless, as the major producer of fentanyl, China has to commit to an effort to control the substance, he said.

“China can develop human intelligence to identify drug flows before they get to the port of departure; it could install chemical detection systems to scan for fentanyl molecules,” Felbab-Brown said.

“Conducting steady and regular scanning of at least some portion of the packages and cargo would help.”

And it makes a lot of sense for China, as the leading supplier of fentanyl-like drugs, to take such pre-emptive actions.

“China does have a major and growing drug consumption problem – in heroin, methamphetamines and cocaine,” Felbab-Brown said. “Consumption of all of these drugs is expanding rapidly in China – it should not assume it is immune from fentanyl abuse.”

Beijing has been working with the US on curbing fentanyl-like drugs flowing from China, including instructing customs and postal services to strengthen the checking and seizures of suspicious parcels sent to the US via particular ports, but China sees cutting demand in the US as the key factor.

“Fentanyl abuse can come to China and become as deadly as in the US,” she said. “For its own sake, it makes sense for China to design effective laws and stringent enforcement, improving its controls from what is in place today.”