They stored the haul, poorly concealed in blue plastic bags and a yellow jerry can, in the back of the customs office. Its owner escaped, slipping away into the sprawl of shacks and hawkers.

Days later, according to two officials involved in the seizure, a top officer from regional headquarters took a closer look at the trove and identified it as the drug methamphetamine. The 81 kg (179 pounds) stash was worth an estimated $12 million or more based on the street price for the drug in Tokyo, where much of it ends up.

The seizure was one of three in Senegal so far this year. It highlights the new and fast-growing role West Africa is playing in the global drug trade, not just as a transit point for drugs but also as a producer of amphetamine-type stimulants (ATS).

Smugglers of Moroccan hashish have long crossed West Africa on their way to Europe or Asia. Over the past decade, the region has also become a major transit point for Latin American cocaine headed to Europe. But local and international officials say West African criminal groups are now producing and exporting hundreds of millions of dollars worth of methamphetamine - or meth - every year, most of it shipped to Asia.

Climate dictates where cocaine, heroin or hashish are produced, but there are no such constraints on meth. The synthetic drug is derived from ephedrine or pseudoephedrine, two medicines that are used to treat ailments from nasal decongestion to asthma. As anyone who has seen the television series "Breaking Bad" knows, meth can be manufactured even with basic equipment and a simple understanding of chemistry. The potential profits are huge: One kilo of meth costs around $1,500 to make in West Africa but sells for around $150,000 in Japan.

The powerful stimulant is smoked, swallowed, snorted or injected by hundreds of thousands of users there, in the United States and elsewhere. The United Nations Office on Drugs and Crime (UNODC) says meth is increasingly popular in East and Southeast Asia. Meth gives users an intense rush, heightens attention and curbs appetite. It is highly addictive. Over time, addicts usually suffer anxiety, weight loss and tooth decay.

A clandestine methamphetamine laboratory is seen inside a compound at Monkey Village in Lagos, Nigeria, in this undated photo taken from a National Drug Law Enforcement Agency (NDLEA) powerpoint presentation provided to Reuters, July 9, 2015.

One reason West Africa is a good production zone, according to law enforcement officials, is the region's weak controls on imports of meth ingredients. Imported legally for use in products such as cold medicine, they can easily be diverted and transformed into meth by boiling, filtering and then combining them with other chemicals.

Pierre Lapaque, head of UNODC in West and Central Africa, puts production of the drug in West Africa at around 1.5 tonnes per year. That's small by world standards – just a little over one percent of the 107 tonnes that was seized around the globe in 2012. But it is up from zero in the region just five years ago.

"It is pretty alarming," Lapaque said.

Nigerian authorities have discovered 10 labs since 2010. Former President Olusegun Obasanjo told Reuters that political leaders needed to wake up to the fact the region had become a producer.

Obasanjo now heads the West African Commission on Drugs and said the production of meth in the region was raising the threat of drug-fuelled instability. "It is now affecting our politics because money earned from drugs is going into politics," he said. "You have drug barons who are now sponsoring politicians, or who (are) in fact going into politics themselves."

Rusty Payne, a spokesman for the U.S. Drug Enforcement Administration, said one sign of the growing importance of West Africa was the arrival of Latin American producers, including Mexicans. Mexican drug gangs play a central role in the meth industry in North America. Payne said Mexicans have helped set up clandestine labs - known as "clan labs" - in Nigeria.

"They are not just mom and pop labs, they are big labs," Payne said. "Mexicans aren't going to come over and train (people) unless they are dealing in large amounts."

Not ready for meth

Africa's place in the synthetic drug market was, until recent years, limited to South Africa, which has a domestic market and feeds the global supply chain.

The surge in production elsewhere on the continent is part of a broader boom in the global amphetamine-type market. UNODC says annual methamphetamine seizures more than doubled between 2010 and 2012.

The first sign that synthetic drugs were being produced in West Africa came in 2009 when chemicals including MDP-2-P, used to make ecstasy, were found at a lab raided in Guinea. UNODC estimates some $100 million of ecstasy could have been produced from the precursors found there.

The same year, a Nigerian expelled from China was arrested with a manual on how to cook meth, said Ahmadu Giade, head of Nigeria's National Drug Law Enforcement Agency.

"Nigeria at that time wasn't prepared for that type of drug because we knew nothing about it," said Giade. He sent a team to South Africa to investigate how police there handled meth labs.

In 2010, Nigerian agents stumbled across a meth lab in a place called Monkey Village. Sunday Drambi Ziramgey, commander of a National Drug Law Enforcement Agency team, was one of the first on the scene. He described a bungalow where each of the four rooms housed a different stage of the cooking process. In the kitchen, they found cooking pots, burners and compressing machines. A web of light bulbs had been strung up to dry the meth.

A 2010 US investigation into cocaine smuggling in Liberia also uncovered plans to produce meth in the country for shipment to the United States and Japan. A 2011 report by Nigerian law enforcement officials, seen by Reuters, details a step-by-step guide for meth production and distribution which was taken from a Nigerian deported from China. The guide included contacts in Ghana, Iran, Thailand and China who would help find couriers and buyers for meth.

A senior DEA official listed Burkina Faso, Cote d'Ivoire, Gambia, Ghana and Guinea-Bissau as possible locations for meth labs.

Mame Seydou Ndour, Senegal's anti-drug tsar, said making meth across the region had multiple advantages. "The transport cost is reduced. There is less risk in Africa. Labour is cheaper here too – with poverty there are plenty of people who are ready to get involved," he said.

The Nigerian connection

As with many other industries, Nigeria dominates meth production in West Africa. It's home to Africa's biggest population and some of the region's most established criminal gangs, according to drugs experts.

Those gangs have connections with experienced Latin American "cooks," such as three Bolivians detained in one lab raid. But Nigerian gangs can now run the trade themselves, and have established global networks to distribute the finished product.

The DEA official said there had been several reported instances in Nigeria this year of 25 to 50 kg of ephedrine being diverted from registered pharmaceutical companies. "This, on top of the smuggled precursors, readily supplies meth production," the official said.

Giade, Nigeria's top anti-drug cop, said most of the precursors used in Nigerian meth production came from India. Some of the chemicals are approved for import by Nigeria's national food and drug regulator, he said, while others are smuggled in illegally, "because we have porous borders." Giade cited the border to the west with Benin as a major weak point.

In 2014 the Nigerian government told the International Narcotics Control Board (INCB) it needed 9.65 tonnes of ephedrine for legitimate businesses. India alone supplied Nigeria with 9.2 tonnes last year, according to a Reuters analysis of official ephedrine exports listed on Indian trade website www.zauba.com, which collates data from ports and customs authorities. It is not clear how much ephedrine Nigeria imported from other suppliers.

"India is legally doing business, but African nations should be checking if the amounts ordered are in line with what is needed by the different factories using ephedrine," said UNODC's Lapaque.

New networks

West African meth production is still far off the levels in Mexico, where officials seized 19 tonnes last year and discovered a string of so-called super labs. But local groups are beginning to make inroads into lucrative markets in Thailand, Malaysia, Indonesia and Japan.

Law enforcement officials say Nigerian criminal groups use extensive networks of human mules. Several officials in West Africa said Nigerians have begun to employ Europeans with clean passports, who are likely to raise less suspicion in Asia. In December 2013, a German man and an Austrian woman were arrested in Jakarta after they were caught having flown in from Dakar with meth hidden in their luggage, local media reported.

Police in London and Paris last year arrested eight Europeans who had left West Africa and were headed to Asia, each carrying 2 to 6 kg of meth, one foreign law enforcement official told Reuters.

In an effort to stop the industry becoming entrenched, Payne said the DEA is helping local officials by detecting and dismantling clandestine labs.

"They basically have a three-headed monster now in Africa," Payne said. "They have the coke problem from South America, the heroin from Afghanistan, and the home-grown meth that is making its way to South Africa and Asia. We're trying to address it as we can, but that is tough."